Cardiac amyloidosis is a condition where abnormal proteins called amyloid fibrils build up in the heart muscle, making it thick and stiff. This stiffness prevents the heart from filling with blood properly, eventually leading to heart failure. It’s more common than previously thought: roughly 11% of patients with a specific type of heart failure (preserved ejection fraction) have underlying amyloid deposits, and autopsy studies have found amyloid in the hearts of 25% of adults over 85.
How Amyloid Damages the Heart
In a healthy heart, the muscle relaxes between beats to fill with blood, then squeezes to pump it out. In cardiac amyloidosis, misfolded proteins deposit in the spaces between heart muscle cells and gradually stiffen the walls. This makes the heart increasingly rigid, so it can’t relax and fill properly, a pattern called diastolic dysfunction.
The damage doesn’t stop at the main pumping chambers. Amyloid can infiltrate the wall between the upper chambers, thicken the heart valves (causing them to leak), and deposit in or around tiny arteries within the heart. That arterial involvement can occasionally cause chest pain or, rarely, a heart attack. Amyloid buildup in the upper chambers also helps explain why atrial fibrillation, an irregular heart rhythm, is so common in people with this disease.
The Two Main Types
Almost all cardiac amyloidosis falls into two categories, each involving a different protein.
ATTR amyloidosis involves transthyretin, a protein made by the liver that normally carries thyroid hormone and vitamin A through the bloodstream. In the “wild-type” form, the protein is genetically normal but becomes unstable with age and misfolds, depositing in the heart. This predominantly affects men over 70. A hereditary form also exists, caused by a gene mutation that makes transthyretin less stable earlier in life. Certain mutations are more common in specific populations; for example, a variant carried by roughly 3-4% of Black Americans increases the risk significantly.
AL amyloidosis (light-chain amyloidosis) is a blood disorder. Abnormal plasma cells in the bone marrow produce excess antibody fragments that misfold and deposit in organs, including the heart. AL tends to progress faster and can affect the kidneys, liver, and nerves simultaneously. It is less common than ATTR but generally more aggressive when it involves the heart.
Symptoms and Early Warning Signs
The most common symptoms are those of heart failure: shortness of breath with activity, swelling in the legs and ankles, fatigue, and difficulty lying flat at night. Because the heart walls thicken without an obvious cause, cardiac amyloidosis is frequently misdiagnosed as high blood pressure-related heart disease or hypertrophic cardiomyopathy, sometimes for years.
What makes this disease unusual is a trail of clues that often appear well before heart failure. Carpal tunnel syndrome, especially when it affects both hands, is a red flag. In one large Japanese study, lumbar spinal stenosis appeared in about 24% of patients and carpal tunnel in about 8%, often surfacing 18 to 19 months before a cardiac amyloidosis diagnosis. Nerve damage causing numbness or tingling in the hands and feet is another early sign. Spontaneous rupture of the biceps tendon has also been linked to amyloid deposits in connective tissue. If you have unexplained heart thickening alongside any of these conditions, amyloidosis should be on the radar.
How It’s Diagnosed
A key clue on echocardiography is a left ventricular wall thickness of 14 mm or greater, especially when the electrical signals on an ECG look paradoxically small. That mismatch between thick walls and low voltage is a classic red flag. The echocardiogram may also show a sparkling or granular texture in the heart muscle.
For suspected ATTR amyloidosis, a nuclear bone scan using a tracer called technetium pyrophosphate (PYP scan) has become the standard non-invasive diagnostic tool. The tracer binds to transthyretin amyloid deposits in the heart. Results are graded on a scale of 0 to 3 based on how much tracer the heart absorbs compared to the ribs. A grade of 2 or 3, combined with a heart-to-lung uptake ratio of 1.5 or higher, is considered a positive result. When there’s no evidence of a plasma cell disorder (which would suggest AL), this scan has a sensitivity of 99% and specificity of 86%, often eliminating the need for a heart biopsy.
Cardiac MRI adds another layer of information. A technique called late gadolinium enhancement reveals characteristic patterns of amyloid infiltration. In ATTR, 90% of patients show a transmural pattern (the entire wall thickness lights up), while in AL the enhancement tends to be concentrated in the inner lining of the heart wall. This distinction can help determine which type of amyloidosis is present. However, cardiac MRI alone cannot confirm a diagnosis of ATTR.
Blood and urine tests to check for abnormal antibody fragments are essential in every case. Even when a PYP scan is positive, ruling out AL amyloidosis matters because the treatment approach is completely different.
Treatment for ATTR Cardiac Amyloidosis
The landmark treatment for ATTR cardiac amyloidosis is tafamidis, a medication that stabilizes the transthyretin protein and prevents it from misfolding. In the pivotal trial published in the New England Journal of Medicine, patients who took tafamidis had a 30% lower rate of death from any cause compared to placebo (29.5% vs. 42.9% over 30 months). Cardiovascular hospitalizations dropped by about 32%. Patients on the drug also experienced less decline in their ability to walk and in their quality of life.
Tafamidis works best when started earlier in the disease course, before extensive damage has occurred. Beyond this medication, standard heart failure management helps with symptoms: carefully dosed diuretics to reduce fluid buildup, and monitoring for dangerous heart rhythms. Some patients eventually need a pacemaker if the amyloid disrupts the heart’s electrical system.
Treatment for AL Cardiac Amyloidosis
Because AL amyloidosis is driven by abnormal plasma cells, treatment targets the blood disorder directly. The most commonly used combination is bortezomib, cyclophosphamide, and dexamethasone. In recent years, adding daratumumab (an antibody that targets plasma cells) to this regimen has dramatically improved outcomes. In a major trial, 53% of patients receiving the four-drug combination achieved a complete blood response, compared to 18% with the three-drug regimen alone. A complete response means the abnormal proteins are no longer detectable in the blood, which halts further amyloid deposition and gives the heart a chance to recover.
Speed matters in AL amyloidosis. Heart involvement is the most dangerous complication, and outcomes improve substantially when the abnormal protein production is shut down quickly. Some patients with early-stage disease may also be candidates for stem cell transplant after initial treatment.
Who Is Most at Risk
Wild-type ATTR cardiac amyloidosis overwhelmingly affects older men. More than 88% of diagnosed patients are male, with an average age of 74. The condition is increasingly recognized as an underdiagnosed cause of heart failure in the elderly. Hereditary ATTR can appear earlier, sometimes in the 50s or 60s, depending on the specific gene mutation.
AL amyloidosis has no strong sex or age predilection, though it typically presents between ages 50 and 70. It accounts for a smaller share of cardiac amyloidosis cases but demands urgent attention because untreated AL with significant heart involvement carries a poor prognosis, with median survival often measured in months rather than years.
Why Early Detection Matters
Cardiac amyloidosis was once considered rare and untreatable, diagnosed mainly at autopsy. That picture has changed dramatically. Non-invasive tools like the PYP scan can now identify ATTR without a biopsy, and effective therapies exist for both major types. The challenge is thinking of the diagnosis in the first place. If you or someone you know has unexplained heart wall thickening, heart failure that doesn’t respond well to standard treatment, bilateral carpal tunnel syndrome, or spinal stenosis alongside cardiac symptoms, amyloidosis deserves consideration. The earlier it’s caught, the more effective treatment can be.