The main cause of a heart attack is a sudden blockage of blood flow to the heart, almost always triggered by the rupture of a fatty deposit (called plaque) inside a coronary artery. When plaque tears open, the body treats it like a wound and forms a blood clot at the site. That clot can partially or completely block the artery within minutes, starving heart muscle of oxygen and causing permanent damage. In the United States, someone has a heart attack every 40 seconds, totaling about 805,000 per year.
How Plaque Builds Up and Ruptures
Heart attacks don’t happen overnight. They’re the end stage of a slow process called atherosclerosis, which can develop over decades. It starts when cholesterol-carrying particles in the blood slip into the walls of coronary arteries and get trapped. The immune system responds by sending white blood cells to clean up the cholesterol, but over time those cells die and form a core of dead, fatty debris inside the artery wall. The body tries to wall off that debris with a fibrous cap, creating what doctors call plaque.
Not all plaques are equally dangerous. The ones most likely to cause a heart attack have a thin, fragile cap covering a large core of soft, cholesterol-rich material. When that thin cap tears, it exposes the inner contents of the plaque to the bloodstream. This material is intensely clot-promoting, and the body reacts within seconds by forming a thrombus (blood clot) at the rupture site. A surge of adrenaline from physical exertion, emotional stress, or other triggers can make this worse by increasing how sticky platelets are and how readily blood clots.
The clot can grow large enough to block the artery entirely, or it can partially block it while pieces break off and lodge further downstream. Either way, the heart muscle beyond the blockage starts dying within 20 to 40 minutes without blood flow.
The Risk Factors That Drive Plaque Buildup
Several conditions accelerate the process that leads to dangerous plaque. Most are within your control.
High cholesterol is the most direct driver. Diets high in saturated fat, trans fat, and cholesterol raise the level of harmful cholesterol particles circulating in your blood. The more of these particles present, the more likely they are to infiltrate artery walls and start forming plaque. Reducing saturated fat intake and, when needed, using cholesterol-lowering medication can slow or even partially reverse this buildup.
Smoking damages the inner lining of blood vessels, making it easier for cholesterol to enter the artery wall. Nicotine also raises blood pressure, while carbon monoxide from cigarette smoke reduces the oxygen-carrying capacity of your blood. Together, these effects accelerate atherosclerosis and make existing plaques less stable.
High blood pressure puts constant mechanical stress on artery walls. Over years, this stress promotes inflammation and thickening of the artery lining, both of which make plaque formation more likely. It also weakens the fibrous caps that hold plaques together, increasing the chance of rupture.
Physical inactivity contributes indirectly by raising your risk of obesity, high blood pressure, high cholesterol, and diabetes, all of which feed into the same plaque-building process. Regular physical activity improves cholesterol balance, lowers blood pressure, and helps the body use insulin more effectively.
Diabetes deserves special mention because high blood sugar damages blood vessels from the inside and promotes inflammation throughout the body. People with diabetes develop atherosclerosis faster and at younger ages than those without it.
Genetics and Family History
Some people develop dangerous plaque buildup despite having a healthy lifestyle, and genetics plays a significant role. One inherited factor is a blood particle called lipoprotein(a), often written as Lp(a). Unlike regular cholesterol, Lp(a) levels are almost entirely determined by your genes, and high levels (above 50 mg/dL) are surprisingly common. Lp(a) contributes to heart attacks through three distinct pathways: it deposits cholesterol into artery walls like regular LDL cholesterol does, it promotes blood clotting, and it increases inflammation that makes existing plaques more likely to rupture.
If male family members had a heart attack or stroke before age 55, or female family members before age 65, that pattern may point toward a genetic predisposition. Your doctor can test Lp(a) with a simple blood draw. While there are currently limited medications specifically targeting Lp(a), knowing your level helps you and your doctor manage every other risk factor more aggressively.
Less Common Causes
A small percentage of heart attacks happen without any plaque rupture at all. One of these is spontaneous coronary artery dissection (SCAD), where a tear develops in the wall of a coronary artery on its own. Blood seeps between the layers of the artery wall and either clots there or creates a flap that narrows the channel, blocking flow to the heart. SCAD often strikes people who have none of the traditional risk factors for heart disease, including no high blood pressure, high cholesterol, or diabetes. It’s more common in women, particularly younger women.
Coronary artery spasm is another uncommon cause. Here, the muscular wall of a coronary artery contracts suddenly and severely, temporarily choking off blood flow even though there may be little or no plaque present. These spasms can be triggered by stimulant drugs, extreme cold, or severe emotional stress, though sometimes they occur without an obvious trigger.
Why Symptoms Differ Between Men and Women
The underlying cause of most heart attacks is the same regardless of sex, but the way the body signals the event can look very different. Men typically experience the “classic” presentation: crushing chest pain or pressure, often radiating to the left arm or jaw. Women can have chest discomfort too, but it’s frequently not the most prominent symptom. Instead, women more often report shortness of breath, nausea, vomiting, back or jaw pain, dizziness, and extreme fatigue. These symptoms sometimes appear during rest or sleep rather than during exertion.
This matters because vague symptoms lead to delays in seeking help. According to the American Heart Association, 64% of women who die suddenly from coronary heart disease had no previously recognized symptoms. About 1 in 5 heart attacks overall are “silent,” meaning the damage occurs without the person realizing it at the time. The heart muscle still dies, and the scarring still increases the risk of future problems, but the event goes unrecognized until it shows up on a later test.
What Actually Determines Your Risk
Understanding the main cause of a heart attack comes down to recognizing that it’s rarely one factor acting alone. Plaque builds up over years from the combined effects of cholesterol levels, blood pressure, blood sugar, smoking, physical activity, and genetics. The heart attack itself is a sudden event, but the conditions that make it possible develop slowly and are often detectable long before they become dangerous.
Of the roughly 805,000 heart attacks that occur annually in the United States, about 605,000 are first-time events. The remaining 200,000 happen in people who have already had one. That gap highlights an important reality: most people who have a heart attack didn’t know they were at high risk until it happened. The risk factors described above are measurable through routine checkups, and addressing even one of them meaningfully reduces the likelihood that plaque will form, grow, and eventually rupture.