Heart attacks happen when blood flow to part of the heart muscle gets blocked, starving that tissue of oxygen. The most common cause is a buildup of fatty deposits inside the coronary arteries that eventually ruptures and triggers a blood clot. But plaque buildup isn’t the only cause. Arterial tears, spasms, genetic factors, and chronic conditions like diabetes all play a role. In the United States, someone has a heart attack every 40 seconds, adding up to roughly 805,000 cases per year.
Plaque Buildup and Rupture
The single most common cause of heart attacks is atherosclerosis, a slow process where cholesterol-rich particles accumulate inside artery walls over years or decades. It starts when LDL cholesterol (the “bad” kind) seeps into the inner lining of a coronary artery. Once there, these particles get chemically modified, which sets off an inflammatory response. White blood cells rush in, swallow the cholesterol, and eventually die, forming a fatty, unstable core inside the artery wall.
Over time, a thin cap of tissue forms over this core. If that cap becomes too thin, it can crack open. When it does, the contents of the plaque are exposed to the bloodstream, and the body reacts the same way it does to a wound: it forms a clot. That clot can partially or completely block blood flow through the artery within minutes, cutting off oxygen to the heart muscle downstream. This is the classic heart attack.
Not every plaque is equally dangerous. The ones most likely to rupture tend to have large, soft fatty cores and very thin outer caps. Plaques that are only moderately narrowing an artery can still be the ones that rupture, which is why some people have heart attacks without ever experiencing warning symptoms like chest pain during exercise.
High Cholesterol, High Blood Pressure, and Diabetes
Several chronic conditions accelerate plaque buildup and make rupture more likely. High LDL cholesterol is the most direct driver, since LDL particles are the raw material that forms plaques. Optimal LDL levels for people without heart disease are below 100 mg/dL. People at intermediate risk are advised to get below 70 mg/dL, and those at higher risk should aim for below 55 mg/dL.
High blood pressure damages artery walls by forcing blood through them with excessive force. That damage creates more entry points for cholesterol to lodge inside the vessel lining, speeding up the entire process. The combination of high blood pressure and high cholesterol is particularly harmful because one condition creates the damage and the other fills it in.
Diabetes adds another layer of risk. Persistently high blood sugar damages blood vessels and the nerves that help regulate heart function. People with type 2 diabetes are significantly more likely to develop coronary artery disease, partly because diabetes often comes alongside high blood pressure, abnormal cholesterol levels, and chronic inflammation. These conditions rarely act alone. They tend to cluster together and compound each other’s effects.
The Role of Inflammation
Inflammation isn’t just a side effect of plaque buildup. It actively drives the process forward and makes existing plaques more dangerous. When the artery wall is inflamed, the thin cap over a plaque weakens faster, making rupture more likely. One way doctors gauge this risk is through a blood test that measures high-sensitivity C-reactive protein (hs-CRP), a marker the liver produces in response to inflammation throughout the body.
An hs-CRP level below 2.0 mg/L is associated with lower heart disease risk. Levels at or above 2.0 mg/L are linked to a higher chance of heart attack. People who have already had one heart attack and still have elevated hs-CRP are more likely to have another. Chronic inflammation can come from many sources: obesity, smoking, gum disease, autoimmune conditions, or even long-term psychological stress.
Genetic Factors
Some people inherit a significantly higher risk of heart attack regardless of their lifestyle. One of the most important genetic factors is lipoprotein(a), often written as Lp(a). This is a type of cholesterol particle whose levels are almost entirely determined by your genes. Unlike regular LDL cholesterol, Lp(a) doesn’t respond much to diet or exercise changes.
High Lp(a) levels, defined as greater than 50 mg/dL, are surprisingly common. Lp(a) contributes to heart attacks in three ways: it builds up in artery walls like LDL does, it promotes increased blood clotting (which can rapidly block a vessel), and it fuels inflammation that makes existing plaques more likely to rupture. People with high Lp(a) are at elevated risk for heart attacks at younger ages, especially if they also have a family history of heart disease. Because Lp(a) isn’t part of a standard cholesterol panel, many people don’t know their level unless they specifically ask for the test.
Coronary Artery Dissection (SCAD)
Not all heart attacks involve cholesterol plaques. In spontaneous coronary artery dissection, or SCAD, a tear develops in the inner wall of a coronary artery. Blood seeps between the layers of the artery wall, forming a clot or flap that pinches the channel shut and blocks blood flow. The result is a heart attack, but the underlying cause has nothing to do with atherosclerosis.
SCAD most commonly affects women in their 40s and 50s, many of whom have no traditional risk factors for heart disease. They may have normal cholesterol, normal blood pressure, and no diabetes. Instead, SCAD is linked to conditions that weaken blood vessel walls, such as fibromuscular dysplasia (a condition affecting medium-sized arteries) and connective tissue disorders like Ehlers-Danlos syndrome and Marfan syndrome. Intense physical exertion and severe emotional distress can trigger SCAD events. Cocaine use also raises the risk.
Coronary Artery Spasm
A coronary artery can temporarily squeeze shut even when there’s no significant plaque inside it. This is called a coronary vasospasm, and if the spasm lasts long enough, it can starve the heart muscle of blood and cause a heart attack. Spasms can happen at rest, often in the early morning hours. Smoking, cocaine use, extreme cold, and severe emotional stress are known triggers. Some people experience repeated spasms over time, a condition sometimes called variant or Prinzmetal angina, which can eventually lead to a full heart attack if a spasm is prolonged or triggers a clot.
Acute Triggers That Set Off a Heart Attack
Most heart attacks happen in people who already have underlying artery disease, but the timing of a specific event is often set off by an acute trigger. In a study of 874 heart attack patients, nearly half identified a trigger that occurred shortly before their event. The most common were emotional stress, physical exertion, lack of sleep, sexual activity, caffeine, and cocaine use.
Anger and anxiety in the two hours before a heart attack carry real consequences beyond just triggering the event. Patients who experienced anxiety right before their heart attack had a 44% higher rate of death over the following ten years compared to those who didn’t. Anger as a trigger was more common in younger patients and those with lower socioeconomic status. These emotional states raise blood pressure and heart rate sharply, increase the stickiness of blood platelets, and can cause a vulnerable plaque to crack open.
Cold weather is another well-documented trigger. Exposure to cold causes blood vessels to constrict, raising blood pressure and forcing the heart to work harder. For someone with narrowed arteries, that extra demand can push the system past its limit.
Smoking and Obesity
Smoking damages artery walls directly, makes blood more prone to clotting, lowers HDL (“good”) cholesterol, and raises LDL cholesterol. It also causes chronic inflammation. The combination means smokers develop atherosclerosis faster and are more likely to have a plaque rupture. The risk drops substantially within a few years of quitting, though it takes longer to fully return to baseline.
Excess body fat, particularly around the abdomen, promotes insulin resistance, raises blood pressure, worsens cholesterol profiles, and keeps inflammation levels chronically elevated. Obesity rarely causes a heart attack on its own, but it amplifies nearly every other risk factor on this list. Losing even a modest amount of weight can meaningfully improve blood pressure, blood sugar, and cholesterol levels.
Less Common Causes
A small number of heart attacks result from causes that don’t fit neatly into the categories above. Blood clots that form elsewhere in the body can travel to a coronary artery and block it. Severe infections or sepsis can put so much stress on the heart that it triggers a cardiac event. Extremely high heart rates from abnormal heart rhythms can overwhelm the heart’s own oxygen supply, particularly in someone with even mild underlying artery disease. Certain autoimmune diseases, including lupus and rheumatoid arthritis, increase heart attack risk through chronic vascular inflammation.
In rare cases, people have heart attacks with no identifiable blockage or structural problem at all. This is sometimes attributed to dysfunction in the very small blood vessels of the heart, a condition that’s more common in women and harder to detect on standard testing.