During a heart attack, a blood clot suddenly blocks one of the arteries supplying your heart muscle, cutting off its oxygen supply. Within minutes, heart cells begin to die. The faster blood flow is restored, the more muscle is saved, which is why every minute counts from the moment symptoms begin.
What Happens Inside the Artery
A heart attack almost always starts with a fatty deposit (plaque) that has been building inside a coronary artery for years, sometimes decades. These plaques sit quietly in the artery wall until one of them becomes unstable. When that happens, the thin cap covering the plaque cracks open, exposing the material inside to your bloodstream.
Your body treats that exposed material the same way it treats any wound: it sends platelets rushing to the site. Those platelets stick together and trigger a clotting cascade that can seal off the artery entirely within minutes. The clot itself is what causes the emergency. Without it, a cracked plaque alone wouldn’t necessarily be dangerous. But when a large clot forms and stays in place, the section of heart muscle downstream is suddenly starved of oxygen.
Once blood flow stops, heart cells can survive in a stressed state for roughly 20 to 45 minutes. Animal studies show that after about 45 minutes of complete blockage, cells can still recover if blood flow returns. But by 90 minutes of total oxygen deprivation, around 90% of the affected muscle cells are dead. That window between “still salvageable” and “permanently lost” is the reason hospitals race to open blocked arteries as fast as possible.
How a Heart Attack Feels
The most common symptom for both men and women is chest pain or pressure, often described as heavy, tight, or crushing. It can radiate into the left arm, jaw, neck, or back. But a heart attack doesn’t always look the way it does in movies.
Women are more likely to experience what doctors call “atypical” symptoms: nausea, vomiting, shortness of breath, dizziness, or pain in the upper back or stomach rather than the classic chest-clutching scenario. Men report chest pain as their primary complaint about 13 to 15% more often than women do. Black and Hispanic women in the United States are even more likely than white women to present with these less obvious symptoms, which can lead to dangerous delays in seeking help.
Women also tend to have warning signs in the days and weeks before a heart attack. The most commonly reported are unusual fatigue, sleep disturbances, anxiety, and shortness of breath. In one study, over 50% of women had noticeable changes in their sleep patterns within four weeks of their heart attack, compared to 32% of men. These prodromal symptoms are easy to dismiss as stress or poor sleep, which partly explains why women tend to arrive at the hospital later after symptoms begin.
Silent Heart Attacks
Not every heart attack announces itself. Data from the long-running Framingham Heart Study found that nearly one quarter of all heart attacks were “silent,” meaning the person either had no symptoms or symptoms so mild they were never recognized as a cardiac event. These are typically discovered later, sometimes years later, when an EKG or imaging test reveals telltale damage patterns on the heart. Silent heart attacks carry the same long-term risks as ones with obvious symptoms, including heart failure and a higher chance of a second event.
What Happens at the Hospital
When you arrive at the emergency room with suspected heart attack symptoms, two things happen quickly: a blood draw and an EKG. The EKG reads the electrical activity of your heart and can reveal whether a major artery is completely blocked. If it is, that’s called a STEMI, the most severe type of heart attack, and the goal is to open the artery within 90 minutes of arrival. This target, known as “door-to-balloon time,” is the national standard of care set by the American College of Cardiology and the American Heart Association.
The blood test looks for proteins called troponins that leak out of damaged heart cells. In a healthy person, troponin levels are essentially zero. During a heart attack, they rise and then fall over the following hours, creating a signature pattern. Both the EKG and blood results together determine the type of heart attack and how aggressively it needs to be treated. Some heart attacks involve a partial blockage rather than a complete one, and those are managed differently, sometimes with medications rather than an immediate procedure.
Complications in the First 48 Hours
The biggest danger in the hours after a heart attack is an abnormal heart rhythm. Damaged heart tissue can misfire electrically, and these rhythm disturbances range from harmless to life-threatening. A fast heart rate occurs in up to 40% of patients. An abnormally slow heart rate affects 15 to 25%, especially when the blockage involves arteries feeding the bottom of the heart. About 6% of hospitalized heart attack patients develop a dangerously fast rhythm originating in the lower chambers of the heart (ventricular tachycardia or fibrillation) within the first 48 hours. This is the kind of rhythm that can cause cardiac arrest and is the reason patients are monitored continuously in the hospital.
Irregular rhythms from the upper chambers of the heart (atrial fibrillation) show up in 6 to 21% of cases. In rare instances, the electrical connection between the upper and lower chambers of the heart can be damaged, causing what’s called a heart block. This occurs in fewer than 5% of patients but is associated with more serious complications, including heart failure and shock.
What to Do If You Witness One
If you or someone near you is having symptoms of a heart attack, call emergency services immediately. While waiting, chewing a regular-strength aspirin (325 milligrams) can help. Chewable aspirin is absorbed faster in the stomach and starts working sooner than a tablet you swallow whole. Aspirin works by making platelets less sticky, which can slow the growth of the clot blocking the artery. It’s not a substitute for emergency care, but it buys time.
If the person loses consciousness and stops breathing, CPR keeps oxygenated blood moving to the brain and other organs until paramedics arrive. Even hands-only CPR (chest compressions without mouth-to-mouth breathing) significantly improves survival.
How the Heart Heals Afterward
Dead heart muscle doesn’t regenerate. Instead, the body replaces it with scar tissue over several weeks to months. This healing process moves through three stages. The first is an inflammatory phase lasting roughly the first week, during which the body clears away dead cells. Next comes a fibrotic phase lasting one to several weeks, when new collagen fibers are laid down. Finally, a remodeling phase stretches over several months as the scar matures and the rest of the heart adapts to its new workload.
How well the heart functions long-term depends largely on how much muscle was lost. Small heart attacks may leave a scar that barely affects pumping ability. Larger ones create a different problem: the scar tissue is weaker than healthy muscle, and over time it can stretch and thin. In some cases, scar tissue thins to as little as 20% of its original thickness. As the scar thins, the wall stress on that area increases, which causes it to thin even more, creating a cycle that can gradually enlarge the heart and reduce its pumping efficiency. This process, called ventricular remodeling, is one of the main ways a heart attack leads to heart failure months or years later.
Cardiac rehabilitation, which combines supervised exercise with lifestyle changes, helps the surviving heart muscle strengthen and can slow or prevent harmful remodeling. Most programs run 12 weeks, and people who complete them have measurably better outcomes than those who don’t. The months after a heart attack are when the heart is actively reshaping itself, making that window a critical time to support recovery.