How ARNI Medications Work to Treat Heart Failure

ARNI stands for angiotensin receptor-neprilysin inhibitor, a class of heart failure medication that works by blocking two harmful pathways at once rather than just one. The only approved drug in the class is sacubitril/valsartan, a combination pill that pairs a neprilysin inhibitor with an angiotensin receptor blocker.¹ Since its approval in 2015, ARNI therapy has reshaped how clinicians manage heart failure with reduced pumping ability, with growing evidence touching kidney protection, blood-sugar control, and blood pressure management in ways that extend well beyond the original indication.

How the Two-in-One Mechanism Works

Your body manages blood pressure and fluid balance through competing systems. One system, the renin-angiotensin-aldosterone system (RAAS), drives blood vessels to tighten and tells the kidneys to hold on to salt and water. The opposing system uses natriuretic peptides, hormones released by the heart that relax blood vessels, push sodium out through the kidneys, and reduce the workload on a struggling heart. In heart failure, the RAAS overdrive overwhelms those protective peptides. Traditional drugs like ACE inhibitors and ARBs attack the RAAS side, but ARNI attacks from both directions simultaneously.

The valsartan half blocks angiotensin II receptors, directly opposing the RAAS. The sacubitril half inhibits neprilysin, an enzyme that chews up natriuretic peptides before they can do their job.² With neprilysin blocked, levels of those beneficial peptides rise, promoting more sodium excretion, blood vessel relaxation, and less harmful remodeling of the heart muscle. Neprilysin also breaks down other substances, including bradykinin, substance P, adrenomedullin, and even some angiotensin peptides, so its inhibition has a broad web of downstream effects.³ That breadth is part of why blocking neprilysin alone would be counterproductive: it would also raise angiotensin levels, which is exactly why the drug pairs the neprilysin inhibitor with an angiotensin blocker.

The Trial That Changed Heart Failure Treatment

The evidence that vaulted ARNI into first-line therapy came from PARADIGM-HF, a trial of over 8,000 patients with heart failure and reduced ejection fraction (meaning the heart’s pumping power was significantly weakened). Patients were randomly assigned to sacubitril/valsartan or enalapril, a well-established ACE inhibitor that had been the standard of care for decades. The trial was stopped early because the benefits of sacubitril/valsartan were so clear that continuing to withhold it from the enalapril group was considered unethical.

Compared with enalapril, sacubitril/valsartan reduced the combined rate of cardiovascular death or heart failure hospitalization by about 20%. Death from cardiovascular causes fell by 20%, death from any cause fell by roughly 16%, and hospitalization for heart failure dropped by 21%.⁴ These benefits held up regardless of what other heart failure medications patients were already taking, including beta-blockers, mineralocorticoid receptor antagonists, and diuretics.⁵ Patients also reported fewer symptoms and better physical function. For a disease in which five-year survival rates rival those of many cancers, these numbers represented a meaningful leap forward.

Starting Treatment During a Hospital Stay

For years, the convention was to stabilize a patient through an acute heart failure episode and then consider switching to sacubitril/valsartan at some point after discharge. The PIONEER-HF trial challenged that approach. Patients hospitalized for acute decompensated heart failure who were hemodynamically stable were started on sacubitril/valsartan before leaving the hospital. Those patients experienced a greater drop in NT-proBNP (a stress marker released by the heart) than patients given enalapril, and the drug was well tolerated even in that vulnerable period.⁶ Rates of worsening kidney function, dangerous potassium elevations, low blood pressure, and angioedema were similar between the two groups. An extension of that trial reinforced that in-hospital initiation was safe and led to better outcomes than waiting.⁷ One practical wrinkle: patients switching from an ACE inhibitor must wait at least 36 hours between stopping the ACE inhibitor and starting sacubitril/valsartan, because overlap between the two raises the risk of angioedema.⁸ Patients already on an ARB can switch without a washout.

When Ejection Fraction Is Preserved

Not all heart failure involves a weak pump. In heart failure with preserved ejection fraction (HFpEF), the heart squeezes normally but is too stiff to fill properly. Treating HFpEF has historically been frustrating because most drugs that work in reduced ejection fraction fail here. ARNI came tantalizingly close to breaking that pattern. The PARAGON-HF trial compared sacubitril/valsartan to valsartan alone in HFpEF patients and found a trend toward fewer hospitalizations and cardiovascular deaths, but the result narrowly missed statistical significance.⁹

That near-miss, however, masks a more interesting pattern. When researchers looked at subgroups, patients whose ejection fraction sat below the study’s median of 57% saw a clear benefit from sacubitril/valsartan, with a hazard ratio suggesting a roughly 22% reduction in the primary endpoint.¹⁰ Women also appeared to benefit more than men. The interpretation now favored by many cardiologists is that ARNI helps patients whose hearts have at least some degree of systolic impairment, even if their ejection fraction technically qualifies as “preserved.” The drug’s indication has since been expanded in some countries to reflect this middle ground.

Kidney Protection

Heart failure and kidney disease feed each other in a vicious cycle: a weak heart delivers less blood to the kidneys, and failing kidneys retain fluid that further burdens the heart. ARNI appears to slow the kidney side of this spiral. In the PARAGON-HF cohort, patients on sacubitril/valsartan had about half the rate of composite renal events (a steep decline in kidney filtration or end-stage kidney disease) compared to those on valsartan alone, and the annual decline in kidney function was smaller.¹¹

A recent systematic review and meta-analysis pooling data across multiple trials put numbers on the broader picture: ARNI therapy was associated with roughly a 31% reduction in renal impairment compared to standard ACE inhibitor or ARB treatment, and a 37% reduction in the odds of severe kidney function decline or end-stage renal disease. That said, rates of acute worsening kidney function and hyperkalemia were similar between ARNI and the older drugs.¹² The kidney benefit likely traces in part to the natriuretic peptide boost: these peptides dilate the blood vessels feeding the kidneys and promote sodium excretion in ways that reduce the long-term strain on kidney tissue.

Reverse Cardiac Remodeling

When the heart struggles to pump blood for months or years, the muscle walls stretch and thicken in ways that make the problem progressively worse. This process, called cardiac remodeling, is one of the central drivers of heart failure deterioration. ARNI can partially reverse it. In one study, patients started on sacubitril/valsartan saw their ejection fraction rise from a mean baseline of about 25% to roughly 30% within just three months, along with measurable shrinkage in the dimensions of the heart’s main pumping chamber and a drop in left ventricular mass.¹³ A separate study tracking patients over 12 months showed ejection fractions climbing from around 28% at baseline to 37-38%, irrespective of whether patients had type 2 diabetes.¹⁴ These structural improvements matter because they correlate with reduced symptoms, fewer hospitalizations, and better long-term survival.

Blood Pressure Lowering and Arterial Stiffness

ARNI was developed for heart failure, but it lowers blood pressure more effectively than conventional ARBs alone, which has attracted interest in treating hypertension, especially resistant cases. In a randomized trial comparing sacubitril/valsartan to olmesartan (a potent ARB) in patients with essential hypertension, both doses of sacubitril/valsartan produced significantly greater reductions in systolic blood pressure. The advantage was particularly striking in patients whose blood pressure failed to dip normally at night, a pattern linked to higher cardiovascular risk.¹⁵ A systematic review of studies in resistant hypertension found statistically significant blood pressure drops across all included studies, with 24-hour reductions in the range of 16/7 to 17/9 mmHg.¹⁶

Beyond just the numbers on a blood pressure cuff, ARNI affects the stiffness of the arteries themselves. In the PARAMETER study of elderly patients with systolic hypertension and stiff arteries, sacubitril/valsartan reduced central aortic systolic pressure by about 3.7 mmHg more than olmesartan and also lowered central pulse pressure, which reflects aortic stiffness.¹⁷ Animal research suggests this may involve a direct effect on the artery walls. In mice, sacubitril/valsartan reduced structural aortic stiffness more than valsartan alone, partly through an antifibrotic action on smooth muscle cells that produce collagen in the artery wall, an effect that appeared independent of the blood pressure reduction itself.¹⁸

Side Effects Worth Knowing About

The most common concern with ARNI in practice is low blood pressure. A meta-analysis of randomized trials found that hypotension occurred roughly 1.8 times more often in patients on sacubitril/valsartan than in those on an ACE inhibitor or ARB.¹⁹ For most patients, this is manageable with dose adjustments or timing changes, but it explains why doctors typically start at a low dose and titrate upward. Safety profiles were otherwise comparable between ARNI and the older drugs in those pooled trials.

Angioedema, a rapid swelling of tissue beneath the skin (especially around the face and throat), was a major theoretical worry when the drug was in development. Neprilysin degrades bradykinin, the same peptide implicated in ACE inhibitor-related angioedema, so blocking neprilysin could theoretically make swelling worse. In practice, sacubitril/valsartan has been associated with a lower risk of angioedema than ACE inhibitors. One large analysis found that patients newly started on sacubitril/valsartan had an 82% lower hazard of angioedema compared to ACE inhibitor users.²⁰ The likely explanation is that the drug replaces the ACE inhibitor entirely with an ARB, and ARBs raise bradykinin far less than ACE inhibitors do.²¹ The mandatory 36-hour washout when switching from an ACE inhibitor exists precisely to avoid any window of double-bradykinin accumulation.

Hyperkalemia (elevated potassium) deserves nuance. A single-center study found that potassium levels above 5.0 mmol/L occurred in over 44% of patients within three months of starting sacubitril/valsartan, though clinically significant levels above 5.5 mmol/L were much less common, and only about 1% of patients stopped the drug because of potassium issues.²² In PARADIGM-HF, severe hyperkalemia was actually less common in patients on sacubitril/valsartan than in those on enalapril, even among patients also taking a mineralocorticoid receptor antagonist (a drug class notorious for raising potassium).²³ The natriuretic peptide effect promotes potassium excretion through the kidneys, which may partly offset the potassium-retaining tendencies of the angiotensin blocker. Routine electrolyte monitoring is still standard practice, but the overall potassium profile of ARNI is no worse than what was already familiar with older heart failure drugs.

The BNP Lab Value Puzzle

Doctors routinely track BNP or NT-proBNP blood levels to gauge how well heart failure treatment is working. Higher values generally mean the heart is under more stress. ARNI creates a peculiar wrinkle here. Because neprilysin normally breaks down BNP, blocking neprilysin causes BNP levels to rise, even as the patient’s heart improves. At the same time, NT-proBNP (a different fragment produced alongside BNP but not broken down by neprilysin) falls as the heart gets better.²⁴

This divergence has caused confusion in clinical practice. A doctor who sees rising BNP in a patient recently started on sacubitril/valsartan might worry that heart failure is worsening, when in fact the drug is working as intended. NT-proBNP is the more reliable tracking marker for patients on ARNI. There was even debate about whether the BNP rise reflected a genuine biological change or was partly an artifact of laboratory assay characteristics, but subsequent analysis found that BNP retains its prognostic accuracy for cardiovascular outcomes even while on ARNI therapy, comparable to NT-proBNP.²⁵ The practical takeaway: clinicians should prefer NT-proBNP for monitoring trends, but an isolated BNP result is not meaningless.

After a Heart Attack

Given the remodeling benefits of ARNI, researchers tested whether starting it early after a heart attack could prevent progression to heart failure. The PARADISE-MI trial enrolled patients who had experienced a heart attack complicated by reduced ejection fraction or lung congestion and compared sacubitril/valsartan to ramipril (an ACE inhibitor). The primary result was a disappointment: there was no statistically significant difference in the combined rate of cardiovascular death or incident heart failure over a median follow-up of 22 months.²⁶

The picture is not entirely negative, though. A secondary analysis using a different statistical method (called a win ratio) that weighs clinical events hierarchically found sacubitril/valsartan superior to ramipril.²⁷ Another analysis specifically examining coronary events found that sacubitril/valsartan reduced the composite of coronary outcomes by about 14% compared to ramipril.²⁸ The honest summary is that ARNI does not clearly beat a well-chosen ACE inhibitor in the post-heart-attack setting the way it does in established heart failure. Patients who go on to develop reduced ejection fraction after a heart attack still have a strong rationale for switching.

Effects on Blood Sugar and Diabetes Risk

An unexpected finding across ARNI trials has been a consistent improvement in blood sugar control. Among patients with diabetes and heart failure in the PARADIGM-HF trial, sacubitril/valsartan lowered HbA1c (a three-month average of blood sugar) by about 0.14% more than enalapril over three years. The need to start insulin was 29% lower in the sacubitril/valsartan group.²⁹ In the PARAGON-HF trial of HFpEF patients with diabetes, the HbA1c reduction compared to valsartan alone was larger, around 0.24% at 48 weeks.³⁰

A meta-analysis pooling the data went further: compared to placebo, sacubitril/valsartan reduced the risk of developing new-onset diabetes by about 22% across all patients studied, and the reduction was even larger when restricted to heart failure populations. The likely mechanism involves natriuretic peptides, which enhance insulin sensitivity, promote fat breakdown, and may directly affect pancreatic insulin secretion. There is a flip side, however: the same meta-analysis found that sacubitril/valsartan was associated with a higher risk of hypoglycemia (low blood sugar episodes), particularly in patients with HFpEF.³¹ For patients on insulin or sulfonylureas, starting ARNI may mean their existing diabetes medications become too aggressive and need adjustment.

The Brain Safety Question

Neprilysin is one of the enzymes that breaks down amyloid-beta peptides in the brain, the same proteins that accumulate in Alzheimer’s disease. Blocking neprilysin systemically raised a logical concern: could ARNI accelerate amyloid buildup in the brain and contribute to dementia? This question has received serious scrutiny, and the evidence so far is reassuring.

A dedicated study in healthy volunteers measured cerebrospinal fluid levels of amyloid-beta species after sacubitril/valsartan treatment and found no significant change in the aggregation-prone forms (Aβ 1-42 and Aβ 1-40). There was an increase in a soluble form (Aβ 1-38), but that species is not implicated in amyloid plaque formation, and its levels did not correlate with the amount of active drug reaching the cerebrospinal fluid.³² In a prespecified cognitive analysis of the PARAGON-HF trial, patients taking sacubitril/valsartan showed virtually no difference from the valsartan group on a standard cognitive screening test over 96 weeks. Rates of clinically meaningful cognitive decline, scores dropping below the dementia threshold, and dementia-related adverse events were all similar.³³

Blood-based biomarkers tell a more mixed story. One study in patients with reduced ejection fraction found that Aβ40 levels rose in the blood shortly after starting sacubitril/valsartan, while Aβ42 stayed stable, resulting in a reduced Aβ42/Aβ40 ratio. Neurofilament light chain, a marker of nerve damage, increased modestly at one year. Total tau, another neurodegeneration marker, did not change.³⁴ Interpreting blood-based amyloid markers is tricky, because peripheral neprilysin inhibition could shift amyloid clearance dynamics in the blood without necessarily reflecting what is happening in the brain. The clinical cognitive data, which is ultimately what matters to patients, remains clean.

Real-World Adherence and Cost

Clinical trials use carefully selected patients and close monitoring, so the drug’s real-world performance matters. A large French claims-database study following over 100,000 patients found that about 83% of patients were still taking sacubitril/valsartan at 12 months. Older patients (75 and above) had lower persistence at about 79%, and roughly 3% of all patients stopped the drug in connection with a hospitalization for an adverse event.³⁵ A study of Medicare beneficiaries in the United States found five distinct adherence patterns: about 54% were consistently adherent, while the remaining 46% fell into groups ranging from immediate discontinuation within three months to intermittent use. Black patients and those in socioeconomically disadvantaged areas were more likely to have suboptimal adherence, while receiving a prescription from a cardiologist rather than a generalist was associated with better adherence.³⁶

Cost is a genuine barrier. Sacubitril/valsartan is far more expensive than generic enalapril. Multiple cost-effectiveness analyses across different countries have found it worth the premium in heart failure with reduced ejection fraction: a UK analysis estimated a cost per quality-adjusted life year gained of about £17,100, a figure well below standard willingness-to-pay thresholds.³⁷ One Italian analysis even found sacubitril/valsartan dominant, meaning it both saved money (by reducing hospitalizations) and improved outcomes.³⁸ Results vary by country and healthcare system. In Thailand, the cost per quality-adjusted life year slightly exceeded the local willingness-to-pay threshold.³⁹ With generic versions beginning to reach some markets, the economics are shifting.

Children With Heart Failure

Pediatric heart failure is rare but devastating, and effective treatments are scarce. The PANORAMA-HF trial tested sacubitril/valsartan against enalapril in children ranging from newborns to teenagers with heart failure from systemic left ventricular dysfunction. At one year, the primary endpoint (a global ranking incorporating death, heart failure events, symptom severity, and biomarker changes) did not differ significantly between the two drugs. Both groups improved clinically, and the safety profile in children was acceptable, with similar adverse event rates.⁴⁰ The result was not the clear win that PARADIGM-HF was in adults. One interpretation is that pediatric heart failure has different underlying causes (often congenital structural problems rather than acquired cardiomyopathy), and the biology may not respond to neprilysin inhibition the same way adult hearts do. The drug is still used in some pediatric cases off-label, particularly when standard therapy is failing, but the evidence base is thinner than in adults.

Long-Term Outcomes Outside of Trials

Real-world registries with follow-up extending beyond five years are beginning to paint a picture of how ARNI performs in the messier landscape of everyday clinical practice, where patients have more comorbidities and less consistent monitoring than trial participants. One such study found that ARNI initiation was associated with marked improvement in functional status, with the rate of cardiovascular and heart failure hospitalizations declining by more than 26% compared to the period before ARNI was started. All-cause mortality remained stable, with no signal of excess risk in elderly patients or those with advanced disease.⁴¹ Serious adverse events like significant hypotension, kidney problems, or hyperkalemia were uncommon and consistent with what the clinical trials had already shown. These findings matter because they address a question trials cannot fully answer: does the drug hold up when prescribed by community cardiologists to patients who might have been excluded from the original studies?