Heart attacks happen when blood flow to part of the heart muscle gets cut off long enough for that tissue to start dying. The most common cause is a buildup of fatty plaque inside a coronary artery that suddenly ruptures, but it’s not the only one. Several other conditions, some genetic and some lifestyle-driven, can trigger a heart attack even in people who seem otherwise healthy.
How Most Heart Attacks Actually Happen
The classic heart attack starts years before any symptoms appear. Cholesterol and fat slowly accumulate inside the walls of the coronary arteries, forming deposits called plaque. Over time, a thin fibrous cap forms over each deposit, separating it from the bloodstream. The trouble begins when that cap weakens.
As lipids build up inside the plaque, they create dramatically increased mechanical stress on the cap. At the same time, the fat accumulation triggers inflammation, which further weakens the cap’s structural support. This combination of rising pressure and eroding strength eventually causes the cap to crack open. When it does, the body treats it like any wound: it forms a blood clot. But inside an artery, that clot can partially or completely block blood flow. Within minutes, the heart muscle downstream begins to starve for oxygen, and cells start to die. That’s the heart attack.
Not every plaque rupture causes a full blockage. Some clots are small and dissolve on their own. Others grow large enough to seal off the artery entirely. The size and location of the blockage determine how much damage the heart sustains.
High Blood Pressure
Persistently elevated blood pressure damages artery walls over time, making them stiffer and more prone to plaque buildup. The 2025 guidelines from the American Heart Association and American College of Cardiology define Stage 1 hypertension as a reading of 130 to 139 systolic or 80 to 89 diastolic. Stage 2, which carries higher risk, starts at 140 systolic or 90 diastolic.
High blood pressure forces the heart to work harder with every beat. That extra workload thickens the heart muscle in ways that reduce its efficiency and increases the stress on artery walls throughout the body. For many people, blood pressure creeps up gradually over decades without obvious symptoms, which is why it’s often called a silent risk factor.
Cholesterol and Lipid Levels
LDL cholesterol is the primary raw material for artery plaque. The higher your LDL, the more cholesterol is available to infiltrate artery walls and fuel that buildup. For people who have already had a heart attack or are at very high risk of one, current guidelines recommend keeping LDL below 55 mg/dL to reduce the chance of a second event.
There’s also a lesser-known particle called lipoprotein(a), or Lp(a), that’s almost entirely determined by your genes. About one in five people has elevated levels. If your Lp(a) is 125 nmol/L (50 mg/dL) or higher, it promotes both clotting and inflammation, raising your risk of heart attack, stroke, and other cardiovascular problems. Unlike regular cholesterol, Lp(a) doesn’t respond much to diet or exercise changes, and most people don’t know their level because it’s not part of a standard cholesterol panel. You typically need to ask for the test specifically.
Diabetes and Blood Sugar
Chronically elevated blood sugar damages blood vessels from the inside, accelerating plaque formation and making existing plaque less stable. A large population study of over 600,000 Canadian adults found that cardiovascular risk begins to climb at surprisingly modest blood sugar elevations, even in people without a diabetes diagnosis. Men with an HbA1c of 5.5% to 5.9% (still considered “normal” by many standards) already showed a 12% higher risk of cardiovascular hospitalization compared to those at 5.0% to 5.4%. Women saw increased risk starting at 6.0%.
At HbA1c levels of 6.5% or higher, the threshold for a diabetes diagnosis, men had a 79% higher risk of cardiovascular hospitalization and women had a 51% higher risk. This means the relationship between blood sugar and heart attack risk isn’t binary. It’s a gradient that starts well before someone is formally diagnosed with diabetes.
Chronic Inflammation
Inflammation plays a central role in every stage of plaque development, from the initial fatty streak to the final rupture. It’s not just a bystander. Inflammatory cells actively weaken the fibrous cap that holds plaque together, and inflammatory signals recruit more immune cells to the area, creating a cycle that destabilizes the artery wall.
One way to gauge this risk is through a blood marker called high-sensitivity C-reactive protein, or hs-CRP. A level below 2.0 mg/L is associated with lower heart disease risk, while 2.0 mg/L or above signals higher risk. Chronic inflammation can stem from many sources: obesity (especially abdominal fat, which is metabolically active), autoimmune conditions like rheumatoid arthritis or lupus, gum disease, poor sleep, and ongoing psychological stress. Addressing the underlying source of inflammation matters as much as treating cholesterol numbers.
Coronary Artery Spasms
Not every heart attack involves plaque. A coronary artery spasm is a sudden, temporary tightening of the artery wall that can choke off blood flow even in arteries with no significant buildup. These spasms often strike while you’re resting, which distinguishes them from the exertion-related chest pain typical of clogged arteries.
Common triggers include tobacco use, cocaine or amphetamine use, exposure to cold temperatures, and extreme emotional stress. Many spasms are brief and go unnoticed, but a prolonged or severe spasm can cause the same oxygen deprivation and muscle damage as a plaque-related blockage. This is one reason heart attacks sometimes occur in younger people with clean-looking arteries on imaging.
Spontaneous Coronary Artery Dissection
Spontaneous coronary artery dissection, or SCAD, occurs when the inner layers of a coronary artery tear apart, allowing blood to collect between the layers and compress the channel that carries blood to the heart. It has nothing to do with cholesterol buildup.
SCAD disproportionately affects younger women. Research published in JACC: Cardiovascular Interventions estimates that SCAD accounts for up to 35% of heart attacks in women under 50. It’s also linked to pregnancy, extreme physical exertion, and connective tissue disorders. Because SCAD patients often don’t fit the typical heart attack profile (older, male, overweight, high cholesterol), their symptoms are sometimes initially dismissed or misdiagnosed.
Lifestyle and Behavioral Triggers
Several everyday factors can set the stage for a heart attack or act as the final trigger in someone already at risk. Smoking is one of the most potent. It damages the endothelium (the inner lining of arteries), raises blood pressure, reduces oxygen in the blood, and makes platelets stickier and more prone to clotting. Quitting smoking cuts heart attack risk substantially within the first year.
Physical inactivity, a diet high in processed foods and added sugars, and obesity each independently raise cardiovascular risk. They also tend to cluster together and amplify one another. Chronic stress and sleep deprivation increase cortisol and inflammatory markers, contributing to both high blood pressure and plaque instability. Heavy alcohol use raises blood pressure and can trigger abnormal heart rhythms that compromise blood flow.
Silent Heart Attacks
About 45% of heart attacks are “silent,” meaning they occur without the classic crushing chest pain most people expect. According to Harvard Health, silent heart attacks strike men more often than women, though women are more likely to experience atypical symptoms like nausea, jaw pain, or unusual fatigue rather than the textbook pressure in the chest.
A silent heart attack still damages heart muscle. Many people discover they had one only when a later EKG or imaging study reveals scarring. That damage increases the risk of heart failure and a future, more severe heart attack. This is part of why routine cardiovascular screening matters, particularly if you have multiple risk factors. The absence of dramatic symptoms doesn’t mean the absence of harm.