A myocardial infarction is the medical term for a heart attack. It happens when blood flow to part of the heart muscle gets blocked, usually by a blood clot forming inside a narrowed coronary artery. Without blood supply, that section of heart tissue starts to die. In the United States, someone has a heart attack every 40 seconds, adding up to roughly 805,000 cases per year. About 605,000 of those are first-time events.
What Happens Inside the Heart
Your heart muscle needs a constant supply of oxygen-rich blood delivered through the coronary arteries. Over years or decades, fatty deposits called plaque can build up inside these arteries, narrowing them. A heart attack typically occurs when one of those plaques ruptures. The body treats the ruptured plaque like a wound and forms a blood clot over it. That clot can partially or completely block the artery, cutting off blood flow to the heart muscle downstream.
The longer the blockage lasts, the more heart tissue dies. This is why speed matters so much in treatment. Heart muscle that loses its blood supply for more than about 20 minutes begins to sustain permanent damage, and the window for preventing serious harm narrows with every passing minute.
Classic and Atypical Symptoms
The most recognized symptom is chest pain or pressure, often described as a squeezing or heaviness in the center or left side of the chest. This pain can radiate into the left arm, jaw, neck, or back. Many people also experience shortness of breath, cold sweats, nausea, and lightheadedness.
Not everyone gets the textbook version. Women are more likely than men to experience symptoms that seem unrelated to the heart: neck, jaw, shoulder, upper back, or upper stomach pain, unusual fatigue, nausea or vomiting, and heartburn. These symptoms can be vague but more noticeable than any chest discomfort. Women also tend to have symptoms more often while resting or even while asleep, which can delay recognition.
Perhaps most concerning, about 1 in 5 heart attacks are “silent.” The damage occurs, but the person doesn’t realize it at the time. Silent heart attacks are often discovered later during routine testing, and they carry the same long-term risks as ones you feel.
Types of Heart Attack
Emergency teams classify heart attacks based on what an electrocardiogram (ECG) shows. A STEMI (ST-elevation myocardial infarction) produces a specific electrical pattern indicating that a coronary artery is completely or nearly completely blocked. This type requires the most urgent intervention. A NSTEMI (non-ST-elevation myocardial infarction) involves a partial blockage that still damages heart tissue but doesn’t produce that same ECG pattern.
The distinction matters because it determines how quickly you need a procedure to reopen the artery. However, cardiologists increasingly recognize that some complete blockages don’t show the classic STEMI pattern on an ECG, which means some serious heart attacks can initially look less dangerous on paper than they actually are. This is one reason hospitals use blood tests alongside the ECG to confirm a diagnosis.
How a Heart Attack Is Diagnosed
Two tools form the backbone of diagnosis: an ECG and a blood test measuring troponin, a protein that heart cells release when they’re injured. Healthy people have virtually no troponin in their blood, so even small elevations signal heart damage.
Modern high-sensitivity troponin tests can detect very low levels. A reading at or below 6 nanograms per liter at one hour after arrival generally rules out a heart attack. Higher levels with a rising pattern over one to three hours confirm one. The 99th percentile threshold, meaning the level that exceeds what’s found in 99% of healthy people, sits at 27 ng/L for these sensitive assays. Emergency departments typically draw blood on arrival and again one to three hours later to check whether troponin levels are climbing.
Emergency Treatment
For a STEMI, the priority is reopening the blocked artery as fast as possible. The standard procedure is percutaneous coronary intervention (PCI), where a cardiologist threads a thin catheter through an artery in the wrist or groin up to the blockage, inflates a tiny balloon to open it, and places a small mesh tube called a stent to keep it open. Current guidelines set a goal of activating that device within 90 minutes of first medical contact for patients who arrive at or are transported to a hospital equipped for the procedure. For patients who first arrive at a smaller hospital without catheterization capabilities, the target is 120 minutes, including transfer time.
When PCI isn’t available quickly enough, clot-dissolving medication can be given instead. Patients who receive this treatment are then recommended for catheterization and possible stenting within 2 to 24 hours afterward.
For NSTEMIs, the timeline is less compressed but treatment still involves catheterization, blood thinners, and other medications. Most patients undergo a procedure within hours to days depending on their risk level.
Complications After a Heart Attack
The severity of complications depends largely on how much heart muscle was damaged and how quickly treatment was received. Some complications develop within the first 24 hours, while others emerge over weeks or months.
Heart failure is the most common long-term consequence. When a section of heart muscle dies, the remaining muscle has to work harder to pump blood. Over time, the heart can enlarge and weaken, a process called remodeling. Abnormal heart rhythms are another frequent problem, because scar tissue from the infarction can disrupt the electrical signals that coordinate heartbeats.
Cardiogenic shock, where the heart suddenly can’t pump enough blood to meet the body’s needs, is the most dangerous acute complication. It occurs in a small percentage of cases but carries a high mortality rate. A rare but serious mechanical complication involves rupture of the wall separating the heart’s chambers or tearing of the small muscles that anchor the heart valves. Valve problems from this kind of damage typically appear 7 to 10 days after the heart attack, though they can occur earlier.
Recovery and Rehabilitation
Recovery starts in the hospital. Phase 1 of cardiac rehabilitation begins before you’re discharged, with gentle movement and education about medications, diet, and warning signs to watch for. Most people stay in the hospital for two to four days after an uncomplicated heart attack, longer if there were complications or additional procedures.
Phase 2 is the outpatient portion and forms the core of rehab. It typically involves three one-hour sessions per week over 12 weeks, totaling 36 sessions. Each session combines supervised exercise (usually walking on a treadmill or cycling) with monitoring of your heart rate, blood pressure, and rhythm. You’ll also receive guidance on nutrition, stress management, and gradually increasing your activity level. Most insurance plans and Medicare cover this phase.
Phase 3 is self-directed. Once you’ve completed the supervised program, you continue exercising on your own, applying what you’ve learned. The full rehabilitation process takes at least three months, though many people continue building fitness and adjusting habits well beyond that.
Risk Factors You Can and Can’t Control
Some risk factors are fixed: age, sex (men face higher risk at younger ages, though the gap narrows after menopause), and family history of early heart disease. But the major drivers of heart attacks are modifiable. High blood pressure, high cholesterol, smoking, diabetes, obesity, physical inactivity, and chronic stress all increase risk substantially. Coronary heart disease, the underlying condition behind most heart attacks, killed 371,506 people in the United States in 2022.
Of the 805,000 annual heart attacks in the U.S., 200,000 occur in people who have already had one. A prior heart attack roughly doubles your risk of having another, which is why aggressive management of blood pressure, cholesterol, and lifestyle factors after a first event is so critical. The medications prescribed at discharge, typically including blood thinners, cholesterol-lowering drugs, and blood pressure medications, are designed to reduce that repeat risk and are generally continued long-term.