What Is Myocardial Infarction (Heart Attack)?

A myocardial infarction is the death of heart muscle caused by a sudden loss of blood supply, almost always because a clot forms inside a coronary artery and chokes off oxygen to the tissue downstream. The everyday name, “heart attack,” captures the urgency but hides a surprising amount of variety in how these events start, who they affect, what they feel like, and how they are treated. The science behind heart attacks has shifted dramatically in recent decades, and survival has improved by roughly 40 to 50 percent since coronary care units were introduced in the 1960s.

What Actually Happens Inside the Artery

Most heart attacks begin with a fatty deposit, or plaque, that has been building inside a coronary artery wall for years. The plaque itself does not usually cause the infarction; what matters is the moment its surface cracks open. When the plaque ruptures, its fatty core and a substance called tissue factor are suddenly exposed to flowing blood, which triggers a rapid chain reaction that forms a clot at the site.¹ That clot can partially or completely block the artery. If blood flow drops enough, heart muscle cells downstream begin to swell, lose their ability to function, and eventually die.²

The amount of muscle that dies depends on which artery is blocked, where the blockage sits, how complete it is, and how quickly blood flow is restored. A clot in the left anterior descending artery, which supplies the large front wall of the heart, typically damages more muscle than a clot in a smaller branch. Plaque rupture can also be clinically silent, meaning a small clot forms but dissolves or only partially narrows the vessel without causing noticeable symptoms.¹ This is one reason people sometimes show evidence of old heart damage on imaging they never knew about.

Recognizing the Symptoms

The classic presentation is a heavy, squeezing pressure in the center of the chest, sometimes described as an elephant sitting on your ribcage. That pain can spread into the left arm, the jaw, the neck, or the back. Sweating, nausea, and shortness of breath often accompany it. But what many people do not realize is that the textbook picture better describes the average man’s experience than the average woman’s.

Women having a heart attack are more likely to present with nausea or vomiting, shortness of breath, and pain between the shoulder blades rather than classic central chest pain.³ A large meta-analysis found that women had about 30 percent lower odds of reporting chest pain compared with men, and were more likely to report fatigue, neck pain, dizziness, and jaw pain.⁴ That said, chest pain was still the most common symptom in both sexes, occurring in roughly three quarters of women and four fifths of men.³ The overlap is real, and the differences are a matter of degree rather than entirely separate symptom profiles.

Women also tend to experience prodromal symptoms, such as unusual fatigue, in the days before the event, and they take longer on average to get to a hospital after symptoms begin.⁵ Men, on the other hand, are more likely to have a “silent” heart attack, one that either produces minimal symptoms or gets mistaken for something else.⁵ Both patterns lead to delay, which costs heart muscle.

STEMI and NSTEMI

When you arrive at an emergency department with suspected heart damage, one of the first things doctors look at is the electrocardiogram, or ECG. Based on a specific pattern called ST-segment elevation, heart attacks are split into two broad categories. An ST-elevation myocardial infarction, or STEMI, typically means the artery is completely blocked and the damage extends through the full thickness of the heart wall. A non-ST-elevation myocardial infarction, or NSTEMI, usually reflects a partial blockage or damage limited to the inner layer of heart muscle.⁶

This distinction is not just academic; it determines the speed of treatment. A STEMI triggers an emergency protocol for immediate reperfusion, meaning the artery needs to be reopened as fast as possible, usually by threading a catheter into the blocked vessel and inflating a tiny balloon to crush the clot (a procedure called percutaneous coronary intervention, or PCI). NSTEMI patients go through a risk-stratification process to determine how urgently they need that same procedure.⁷ Both conditions share a similar underlying cause, but the timing of intervention differs considerably.

The ECG pattern also gives clues about which artery is affected. In one study of patients with a single blocked vessel, every case of anterior STEMI involved the left anterior descending artery, while most inferior STEMIs traced to the right coronary artery.⁸ This kind of geographic mapping helps catheterization teams anticipate what they will find before they even insert the catheter.

How Doctors Confirm the Diagnosis

The ECG alone is not always definitive. About half of NSTEMI patients in one study did not have clear-cut ischemic changes on their ECG tracing.⁸ That is where blood tests come in. When heart muscle cells die, they release a protein called troponin into the bloodstream. Measuring troponin levels is now the gold standard for confirming heart damage.

Newer high-sensitivity troponin assays have made a major difference. They can detect far smaller amounts of the protein, which means heart attacks can be identified sooner, especially in people who arrive at the hospital within the first few hours of symptom onset. A landmark study found that these sensitive tests performed substantially better than older standard assays during early presentation, with diagnostic accuracy rising from about 76 percent to over 90 percent for patients who showed up within three hours of chest pain.⁹ Current American Heart Association guidelines now recognize high-sensitivity troponin as the preferred biomarker for evaluating acute chest pain.¹⁰

One important nuance: a rise in troponin confirms that heart muscle has been injured, but it does not automatically mean a classic clot-driven heart attack is the cause. Troponin can go up in conditions like severe infections, kidney failure, or extreme physical stress. Doctors have to interpret the blood test alongside the ECG, the patient’s symptoms, and sometimes imaging to piece together the full picture.

Why Every Minute Counts

The phrase “time is muscle” captures the central reality of heart attack treatment. The longer the artery stays blocked, the more heart muscle dies and the worse the long-term outcome. Emergency medical service response times illustrate this starkly: one retrospective study found that each additional minute of response time reduced the odds of survival to hospital discharge by about 6 percent, and that response times under eight minutes roughly doubled the chances of surviving to discharge compared with longer delays.¹¹

For STEMI, the primary goal is reopening the artery through PCI. When catheterization is not immediately available, clot-dissolving drugs (thrombolysis) are an alternative. Both approaches improve survival. A meta-analysis of cardiac-arrest patients with STEMI found that those receiving PCI and those receiving thrombolysis had similar rates of hospital discharge and neurological recovery.¹² That said, PCI is generally preferred when it can be done quickly, because it allows doctors to see exactly where the blockage is and to place a stent that holds the artery open.

There is an irony built into the treatment. Restoring blood flow is absolutely necessary, but the sudden return of oxygen-rich blood can itself cause further injury. Reactive oxygen species, inflammation, and calcium flooding into damaged cells can kill additional muscle that might have survived the initial oxygen deprivation.¹³ Researchers are actively studying ways to reduce this reperfusion injury, but for now, the net benefit of reopening the artery far outweighs the additional damage.

Complications That Can Follow

A large heart attack, or one that goes untreated for too long, can leave the heart structurally compromised. The most feared acute mechanical complications include rupture of the papillary muscles (the small muscular pillars that anchor the heart’s mitral valve), a hole forming in the wall that separates the two pumping chambers, and, in the worst case, rupture of the outer heart wall itself. Each of these carries a serious risk of death and usually requires emergency surgery.¹⁴

The papillary muscle on the back wall of the heart is especially vulnerable because it gets its blood supply from a single artery, whereas the one on the front-side wall has two feeding arteries. If the single-supply artery is the one that gets blocked, that muscle can tear, causing sudden severe leakage of the mitral valve.¹⁵

Even when these dramatic complications do not occur, the heart can quietly remodel over the weeks and months following an infarction. The dead muscle is replaced by scar tissue, and the remaining heart muscle stretches and thins to compensate. The heart’s shape changes from its normal football-like configuration to something rounder and larger, which makes it a less efficient pump.¹⁶ This remodeling process, if it progresses unchecked, is the pathway from heart attack to heart failure.¹⁷

Heart Attacks Without Blocked Arteries

Not every heart attack fits the standard narrative of a clogged artery. About 5 to 6 percent of patients who undergo angiography after an acute infarction turn out to have no significant blockage in their coronary arteries, a condition called MINOCA (myocardial infarction with non-obstructive coronary arteries).¹⁸ The causes are varied and include spasm of the coronary artery, tiny clots or debris traveling from elsewhere, spontaneous tearing of the artery wall, and dysfunction at the level of the smallest blood vessels in the heart.¹⁹

MINOCA is an important diagnosis to get right because treatment depends on the underlying cause. Advanced imaging techniques, both inside the artery (using ultrasound or optical coherence catheters) and outside the heart (using cardiac MRI), can distinguish plaque disruption from coronary spasm from conditions like myocarditis, which is inflammation of the heart muscle that is not ischemic at all.²⁰ Getting the cause wrong means prescribing the wrong medication, or missing a treatable condition entirely.

There is also a separate condition called Type 2 myocardial infarction, where the heart muscle is starved of oxygen not because of a clot but because of a mismatch between supply and demand. A severe infection, a dangerously fast heart rhythm, a major drop in blood pressure, or severe anemia can all push the heart past its limits even when the arteries themselves are relatively healthy.²¹ Managing these patients means fixing the underlying trigger, not rushing to the catheterization lab.

Takotsubo and the “Broken Heart”

One MINOCA mimic that deserves its own mention is Takotsubo cardiomyopathy, sometimes called broken heart syndrome. Triggered by intense emotional or physical stress, it causes a portion of the heart to balloon outward and stop contracting properly. It looks alarmingly like a heart attack on an ECG and troponin levels rise, but angiography reveals clean coronary arteries. It occurs most often in postmenopausal women and is generally reversible, though it can cause transient heart failure.²² The condition underscores how the nervous system and the heart are linked in ways that go well beyond plumbing.

Risk Factors You Can and Cannot Change

The major modifiable risk factors for heart attack are well established: smoking, high blood pressure, high cholesterol, diabetes, obesity, and physical inactivity. A long-running study of middle-aged British men quantified how these interact. Heavy smokers had about two and a half times the risk of death, heart attack, stroke, or diabetes compared with never-smokers. Men with a BMI of 30 or above had roughly double the risk compared with those at a normal weight. Moderate physical activity cut the risk by about 40 percent compared with being inactive, with no additional benefit from exercising harder than that.²³

On the side you cannot change, genetics play a genuine role. One inherited factor that has received growing attention is lipoprotein(a), a cholesterol-carrying particle whose blood levels are largely determined by your genes rather than your diet or lifestyle. Elevated lipoprotein(a) is an independent driver of cardiovascular disease.²⁴ High levels have been linked to premature coronary heart disease, and because standard cholesterol-lowering drugs like statins do not reduce lipoprotein(a), it often goes unrecognized as a risk factor even in otherwise health-conscious people.²⁵ New therapies targeting lipoprotein(a) directly are in late-stage clinical trials.

Recovery and Cardiac Rehabilitation

Surviving a heart attack is only the beginning. The weeks and months that follow determine how much function you regain and how well you avoid a second event. Cardiac rehabilitation programs, which combine supervised exercise, dietary counseling, and psychological support, have become a core part of post-heart-attack care.²⁶

The evidence supporting these programs is strong. A large meta-analysis found that exercise-based cardiac rehabilitation reduced cardiovascular death by about a quarter, hospital readmissions by roughly a quarter, and the risk of another heart attack by close to a fifth.²⁷ These benefits hold even in older adults. A study comparing elderly and younger patients found statistically similar improvements in exercise capacity, body composition, and cholesterol profiles after completing a rehabilitation program.²⁸

Long-term medications also play a critical role. For patients with standard clot-driven heart attacks, the usual cocktail includes a blood thinner, a statin, a blood-pressure-lowering drug, and sometimes a beta-blocker to ease the heart’s workload. Even for MINOCA patients, observational data suggest that statins and drugs that block the angiotensin system offer long-term survival benefits, though large randomized trials to confirm this are still needed.²⁹

Environmental Triggers and Disparities in Care

Heart attacks do not happen in a vacuum, and some external triggers are less obvious than stress or exertion. Extreme temperatures, both very cold and very hot, are associated with increased risk of STEMI. Air pollution adds to the picture: short-term spikes in fine particulate matter appear to increase STEMI risk, while nitrogen dioxide exposure is more strongly associated with delayed NSTEMI events.³⁰ These findings reinforce that cardiovascular risk is shaped by the environment you live in, not just your personal habits.

Where you live also affects the care you receive. A study of U.S. communities found that patients in the most socioeconomically advantaged areas were about 20 percent more likely to receive same-day PCI for a heart attack compared with those in the most disadvantaged communities, and had roughly 19 percent lower 30-day mortality.³¹ These gaps are not about biology. They reflect differences in proximity to hospitals with catheterization labs, availability of specialists, insurance barriers, and the speed at which patients present for care. The biology of a heart attack is the same regardless of zip code; the survival odds are not.