During a heart attack, a blood clot suddenly blocks one of the arteries feeding your heart muscle, cutting off its oxygen supply. Within 20 to 30 minutes, the starved muscle cells begin to die. The longer the blockage lasts, the more permanent damage occurs, which is why every minute matters.
How a Blockage Forms
A heart attack doesn’t usually start with a healthy artery. It starts with one that has been quietly narrowing for years. Fatty deposits called plaques build up inside the walls of your coronary arteries, the vessels that wrap around the outside of your heart and deliver its blood supply. You can have significant plaque buildup without knowing it.
The crisis begins when one of these plaques ruptures. The plaque’s outer shell cracks open, exposing its soft, fatty interior to the bloodstream. Your body treats this like a wound. Platelets rush to the site and begin clumping together, triggering a cascade of clotting. The activated platelets also release chemicals that cause the artery to constrict, narrowing it further. Within minutes, a blood clot (thrombus) forms on top of the ruptured plaque. If that clot grows large enough to completely block the artery, blood flow to a section of heart muscle stops.
What’s Happening to the Heart Muscle
Your heart muscle is extraordinarily hungry for oxygen. It beats roughly 100,000 times a day and has almost no ability to store energy reserves, so when blood flow stops, trouble starts fast. The affected muscle cells first lose their ability to contract. Within 30 minutes to an hour, those cells begin to swell and break apart. Their internal structures dissolve. Proteins like troponin leak out of the dying cells and into the bloodstream, which is what doctors detect with blood tests to confirm a heart attack.
The damage spreads outward from the center of the affected zone. Cells closest to the blocked artery die first. Cells at the edges, which may still receive some blood from neighboring vessels, survive longer but are on borrowed time. This is the window where restoring blood flow can save tissue. If the artery stays blocked for several hours, the damage becomes extensive and irreversible.
What It Feels Like
The classic symptom is chest pain or pressure, often described as a squeezing, heavy, or tight sensation in the center or left side of the chest. It can radiate into the left arm, jaw, neck, or back. Many people also experience shortness of breath, cold sweats, nausea, or lightheadedness.
But a significant number of heart attacks don’t follow this script. Women more frequently report tiredness, weakness, anxiety, vomiting, back pain, and neck or jaw pain rather than the textbook crushing chest pressure. People with diabetes are especially likely to have atypical or even painless heart attacks. In painless presentations, shortness of breath is the most common symptom, reported by about 72% of those cases. Sweating, fatigue, and arm or jaw pain are also common, appearing in roughly 58 to 64% of cases. Some people feel only a vague sense that something is wrong, or mistake the symptoms for indigestion.
These atypical presentations are dangerous precisely because they delay treatment. If you or someone near you has unexplained shortness of breath, sudden fatigue, or upper body pain combined with sweating or nausea, treat it as a potential heart attack.
What Happens in the First Minutes
If you think you’re having a heart attack, call emergency services immediately. While waiting, chewing a regular aspirin tablet (325 mg) is one of the most effective things you can do. Chewing rather than swallowing it whole matters: a chewed aspirin inhibits 50% of platelet activity in about 5 minutes, compared to 12 minutes for a tablet swallowed intact. Aspirin won’t dissolve the clot that’s already formed, but it helps prevent the clot from growing larger.
Sit or lie down in whatever position feels most comfortable. Loosen tight clothing. Try to stay as calm as possible, since adrenaline increases the heart’s oxygen demand at exactly the wrong time.
What Happens at the Hospital
The goal of emergency treatment is simple: reopen the blocked artery as fast as possible. For the most severe type of heart attack (called a STEMI, where the artery is completely blocked), the standard treatment is a catheter-based procedure. A thin tube is threaded through an artery in your wrist or groin up to the blockage, where a tiny balloon is inflated to reopen the vessel. A small metal mesh tube called a stent is usually placed to keep it open.
The American College of Cardiology and American Heart Association set 90 minutes as the target from the moment you walk through the hospital door to the moment that balloon is inflated. Faster is better. Every 30-minute delay in restoring blood flow increases the amount of heart muscle that dies permanently.
In hospitals without catheterization capability, clot-dissolving medications given through an IV can serve as a bridge, though the catheter procedure remains the preferred approach when available.
How the Heart Heals Afterward
Unlike a cut on your skin, dead heart muscle doesn’t regenerate. Instead, the body replaces it with scar tissue through a process that unfolds over weeks to months. In the first one to three days, the immune system clears away dead cells in an inflammatory phase. Over the following days to weeks, the body lays down new connective tissue. Over weeks to months, that tissue matures and stiffens into a permanent scar.
This scar tissue keeps the heart wall intact, but it can’t contract like healthy muscle. The remaining healthy muscle has to work harder to compensate. Over time, the heart may enlarge and remodel in response to this extra workload. The scar also interferes with the heart’s electrical system, which can predispose some people to abnormal heart rhythms.
How much function you lose depends on how much muscle was damaged. A small heart attack caught early may leave you with near-normal heart function. A large one that went untreated for hours can lead to significant, progressive heart failure. Cardiac fibrosis has been identified as an independent risk factor for heart failure and sudden cardiac death, regardless of how well the remaining muscle pumps.
Life After a Heart Attack
Most people spend two to four days in the hospital after an uncomplicated heart attack. Recovery at home typically takes several weeks, with a gradual return to normal activities. Cardiac rehabilitation programs, which combine supervised exercise with education about diet and lifestyle, significantly improve outcomes and are recommended for nearly everyone.
You’ll likely be prescribed several medications long-term: a blood thinner to prevent new clots, something to lower cholesterol and stabilize any remaining plaques, and medications to reduce the heart’s workload. These aren’t optional extras. They address the underlying disease that caused the heart attack in the first place, since the plaque buildup that triggered one blockage is almost certainly present in other arteries too.
The size of the scar, the heart’s remaining pumping strength (measured by ejection fraction), and how quickly blood flow was restored all shape the long-term outlook. People who get to the hospital quickly, receive prompt treatment, and commit to rehabilitation and medication have substantially better outcomes than those who delay or skip follow-up care.