MONA isn’t a single drug. It’s a medical acronym that stands for Morphine, Oxygen, Nitrates, and Aspirin, the four treatments traditionally given together during a suspected heart attack. The term has been used for years in medical schools and emergency training as a quick way to remember the first-line response to acute coronary syndrome, which includes heart attacks and related cardiac emergencies. While still widely taught, parts of this protocol have been updated as newer evidence has shown that not all four components are always helpful.
What Each Letter Stands For
Each component of MONA targets a different problem happening during a cardiac emergency:
- M (Morphine): A powerful painkiller used to relieve severe chest pain and reduce anxiety. Pain and stress cause your body to release adrenaline, which makes the heart work harder, exactly the opposite of what you want during a heart attack. Morphine helps calm that stress response.
- O (Oxygen): Supplemental oxygen delivered through a mask or nasal tube, intended to ensure the heart muscle gets enough oxygen when blood flow is compromised.
- N (Nitrates): Usually given as nitroglycerin, a tablet or spray placed under the tongue. Nitrates relax and widen blood vessels, which lowers the heart’s workload and helps relieve chest pain.
- A (Aspirin): Given immediately as a chewable tablet. Aspirin blocks platelets from clumping together, helping to prevent the blood clot causing the heart attack from growing larger.
How These Treatments Work Together
During a heart attack, a blood clot blocks one of the arteries feeding the heart muscle. Every minute that passes without blood flow means more heart tissue is damaged. The MONA treatments address this from multiple angles at once.
Aspirin is the most evidence-backed component. It interferes with the chemical signals that tell platelets to stick together, slowing clot growth. Data shows aspirin use during a heart attack reduces cardiovascular death by roughly 23%. Current guidelines recommend a loading dose of 162 to 325 mg, chewed rather than swallowed whole so it absorbs faster, given as soon as a heart attack is suspected.
Nitroglycerin works by relaxing the smooth muscle in blood vessel walls. At lower doses it primarily widens veins, which reduces the amount of blood returning to the heart and lowers the pressure the heart has to pump against. At higher doses it also widens arteries. The net effect is less strain on the heart and significant pain relief.
Morphine acts on pain receptors in the brain and also has some effect on the cardiovascular system. By controlling pain and anxiety, it reduces the flood of stress hormones that force the heart to beat faster and harder during an already dangerous moment.
Oxygen, in theory, ensures the heart muscle has enough of what it needs most. But as you’ll see below, giving oxygen to everyone having a heart attack turned out to be more complicated than it seemed.
Why Parts of MONA Are Now Controversial
The MONA acronym dates back decades, and more recent research has challenged the routine use of two of its components: morphine and oxygen.
Oxygen was once given to every patient with chest pain, regardless of whether their oxygen levels were actually low. Current guidelines from both the American Heart Association and the European Society of Cardiology now recommend supplemental oxygen only when a patient’s blood oxygen saturation drops below 90%. In patients with normal oxygen levels, giving extra oxygen may not help and could potentially worsen outcomes by constricting blood vessels and generating harmful molecules called free radicals.
Morphine has also been downgraded. European guidelines lowered its recommendation class from “indicated” to “should be considered,” a meaningful step down. The concern is twofold. First, morphine slows down the gut, which delays the absorption of other critical medications. Specifically, it interferes with antiplatelet drugs (blood thinners given alongside aspirin) that need to be absorbed quickly to be effective. Data from large registries found worse outcomes in heart attack patients who received both morphine and these oral blood thinners. Second, by masking pain so effectively, morphine may lead medical teams to underestimate how severe the heart attack actually is and delay more aggressive treatment like emergency catheterization.
Nitroglycerin also has important limitations. It should be used cautiously or avoided entirely in patients having a heart attack that involves the right side of the heart. In one study of patients with right-side involvement during a lower heart attack, about 71% developed dangerous drops in blood pressure after receiving nitrates. Nitroglycerin is also contraindicated in patients who have recently taken certain medications for erectile dysfunction, as the combination can cause a life-threatening blood pressure crash.
What Has Replaced MONA
Modern emergency cardiac care goes well beyond four treatments. Some medical educators have proposed newer, more comprehensive acronyms. One example is THROMBINS2, which expands the list to include blood thinners beyond aspirin, beta-blockers (which slow the heart rate), cholesterol-lowering medications started during hospitalization, and emergency procedures to physically reopen the blocked artery.
The 2025 guidelines from the American College of Cardiology and American Heart Association emphasize that initial treatment should begin immediately when a heart attack is suspected. Aspirin remains the cornerstone, given as soon as possible. Beta-blockers are recommended within the first 24 hours for most patients. Anticoagulation (blood-thinning therapy beyond aspirin) is started at the time of diagnosis, before the patient even reaches the catheterization lab.
Despite its limitations, MONA persists as a teaching tool because it’s simple and captures the core principle of early cardiac care: relieve pain, reduce the heart’s workload, and stop the clot from growing. A review in a major cardiology journal noted that “unfortunately, the mnemonic MONA continues to be used” in settings where students may not learn the important caveats that come with each component. The acronym remains a useful starting point, but treating a heart attack in 2025 involves a much longer, more individualized checklist than four letters can capture.
Aspirin: The One Component That Still Stands
Of all four MONA treatments, aspirin has the strongest and most consistent evidence behind it. It is recommended for virtually all heart attack patients unless they have a known allergy or active bleeding. The 23% reduction in cardiovascular death associated with aspirin use during a heart attack comes from large, well-established trials that have held up over decades of scrutiny.
If you or someone nearby is having symptoms of a heart attack, chewing a regular aspirin (not enteric-coated, which absorbs too slowly) is one of the most impactful things that can happen before emergency services arrive. The other three components of MONA are given by medical professionals who can assess whether each one is appropriate for the specific situation.