There is no single number, because “heart disease” is an umbrella term covering at least six major categories, each containing multiple specific conditions. The World Health Organization groups cardiovascular diseases into coronary heart disease, cerebrovascular disease, peripheral arterial disease, rheumatic heart disease, congenital heart disease, and deep vein thrombosis with pulmonary embolism. Within those categories, dozens of individual diagnoses exist. Between 2017 and 2020, roughly 128 million U.S. adults (nearly half the adult population) had some form of cardiovascular disease.
Coronary Artery Disease
Coronary artery disease is the most common and most deadly category. It develops when fatty deposits build up inside the arteries that supply blood to the heart muscle. The process starts when the inner lining of an artery becomes damaged, allowing cholesterol particles to slip beneath the surface. White blood cells rush in to clean up the cholesterol, but they become overloaded and turn into “foam cells” that form a fatty streak along the artery wall.
Over time, this streak grows into a larger plaque with a soft, fatty core covered by a fibrous cap. If the cap is thin and inflamed, it can rupture, triggering a blood clot that blocks the artery. That blockage is a heart attack. In Europe, coronary heart disease accounts for about 21% of deaths in men and 23% in women, making it the single largest killer within the cardiovascular disease family.
Heart Rhythm Disorders
Arrhythmias are conditions where the heart’s electrical system misfires, causing beats that are too fast, too slow, or irregular. A resting heart rate below 60 beats per minute is classified as bradycardia, while anything above 100 beats per minute at rest is tachycardia. Some people also experience premature beats, a sensation that the heart “skipped” followed by a noticeably stronger thump.
The most common arrhythmia is atrial fibrillation, which affects more than 2.5 million Americans. During atrial fibrillation, the upper chambers of the heart fire chaotically at rates above 400 beats per minute, and the upper and lower chambers fall out of sync. A related condition, atrial flutter, drives the upper chambers at 250 to 350 beats per minute, often because scar tissue disrupts the electrical signal.
Ventricular arrhythmias originate in the lower chambers and tend to be more dangerous. Ventricular tachycardia produces a fast, regular rhythm that may last only seconds or persist long enough to become an emergency. Ventricular fibrillation is the most serious: the lower chambers quiver instead of pumping, and without immediate treatment, cardiac arrest and death can follow within minutes.
Heart Valve Disease
The heart has four valves that open and close with every beat to keep blood flowing in the right direction. Disease can affect any of them in three basic ways:
- Stenosis: The valve leaflets stiffen and narrow, reducing the amount of blood that can pass through.
- Regurgitation: The leaflets don’t close completely, allowing blood to leak backward. This is sometimes called a “leaky valve.”
- Prolapse: Most commonly seen in the mitral valve, this occurs when extra-stretchy leaflets bulge back into the upper chamber during each heartbeat.
Because any of the four valves can develop any of these problems, valve disease alone accounts for a dozen or more distinct diagnoses. Some are mild and never need treatment. Others progressively weaken the heart because it has to work harder to compensate for the faulty valve.
Cardiomyopathy
Cardiomyopathy refers to diseases of the heart muscle itself, and it comes in three main structural forms. Dilated cardiomyopathy is the most common: the lower chambers stretch and weaken, becoming too floppy to pump efficiently. Hypertrophic cardiomyopathy is the opposite problem. The muscle grows abnormally thick, which can block blood from leaving the heart. It is commonly inherited, and close family members of someone diagnosed are typically screened. Restrictive cardiomyopathy is rare. The heart walls stiffen without thickening, so the chambers can’t relax enough to fill with blood between beats.
Heart Failure
Heart failure isn’t a single disease but a syndrome that often results from other types of heart disease, including coronary artery disease, valve problems, or cardiomyopathy. Doctors classify it by how well the heart pumps with each beat, measured as the ejection fraction, the percentage of blood pushed out of the lower chamber each time it contracts.
A normal ejection fraction is roughly 50% or higher. Heart failure with reduced ejection fraction means the heart pumps at 40% or below. Heart failure with mildly reduced ejection fraction falls in the 41% to 49% range. Heart failure with preserved ejection fraction means the number looks normal (50% or above), yet the heart still can’t meet the body’s demands, usually because the muscle is too stiff to fill properly. A fourth category, heart failure with improved ejection fraction, applies when someone’s pumping ability recovers from below 40% to above that threshold after treatment.
Congenital Heart Disease
Congenital heart defects are structural problems present at birth. Simpler defects include holes between the heart’s chambers (called septal defects), a blood vessel that fails to close after birth as it should (patent ductus arteriosus), and a narrowed pulmonary valve. These often cause few symptoms and may resolve on their own or with a single procedure.
Complex defects involve multiple structural problems at once. The most common complex defect is tetralogy of Fallot, a combination of four issues: a narrowed pulmonary valve, a large hole between the lower chambers, a displaced aorta, and thickened muscle in the right ventricle. Babies born with this condition typically appear bluish because not enough blood reaches the lungs for oxygen.
Rheumatic Heart Disease
Rheumatic heart disease stands apart from other categories because it starts with an infection. When strep throat goes untreated, the immune response can trigger rheumatic fever, which inflames and scars the heart valves. The damage is permanent and progressive, often leading to stenosis or regurgitation of the mitral or aortic valve. It remains a significant problem in low- and middle-income countries where access to antibiotics is limited, even though it has become rare in wealthier nations.
How Heart Disease Is Detected
Because so many types of heart disease exist, no single test covers everything. An electrocardiogram (ECG) records the heart’s electrical activity and is the go-to tool for spotting rhythm problems. A Holter monitor is a portable version you wear for a day or more to catch irregular beats that don’t show up during a brief office visit.
An echocardiogram uses ultrasound to create a moving picture of the heart, making it especially useful for evaluating valve function and measuring how well the chambers pump. Stress tests reveal how the heart responds to physical exertion and can expose blockages that don’t cause symptoms at rest. When imaging suggests a blockage, cardiac catheterization threads a thin tube into the heart’s arteries and injects dye to pinpoint exactly where and how severe the narrowing is. Blood tests can detect proteins that leak from damaged heart muscle after a heart attack, along with markers of inflammation and cholesterol levels that signal long-term risk.
Cardiac MRI provides the most detailed structural images and is particularly helpful for diagnosing cardiomyopathy, assessing scar tissue, or evaluating complex congenital defects. A simple chest X-ray can also reveal whether the heart is enlarged, often one of the first clues that something is wrong.