Heart disease damages your heart’s ability to pump blood effectively, and the consequences ripple out to nearly every organ in your body. It killed over 919,000 Americans in 2023 alone, making it the leading cause of death in the United States. But “heart disease” isn’t a single condition. It’s an umbrella term covering problems with blood vessels, heart muscle, heart valves, and electrical signaling, each of which disrupts your cardiovascular system in a different way.
How Arteries Become Blocked
Coronary artery disease is the most common form, responsible for more than 371,000 deaths in 2022. It starts with atherosclerosis, a slow buildup of plaque (a mix of fat, cholesterol, calcium, and other substances) inside the walls of arteries that supply your heart muscle with oxygen-rich blood.
This process begins when the inner lining of an artery gets damaged, often by high blood pressure, smoking, or high cholesterol. White blood cells rush to the injury site and trigger inflammation. Over years, fatty deposits accumulate and the artery wall grows thicker and stiffer. The opening narrows, leaving less room for blood to flow. Think of a four-lane highway gradually reduced to a single lane: blood can still get through, but barely enough to meet demand, especially during exercise or stress.
The real danger comes when plaque ruptures. A blood clot forms at the rupture site and can block the artery entirely, cutting off oxygen to a section of heart muscle. That’s a heart attack. Without blood flow, heart cells begin dying within minutes. By 90 minutes of complete blockage, the damage is severe, and after three hours nearly all affected tissue is nonviable. The faster blood flow is restored, the more muscle can be saved.
What Happens to the Heart Muscle
After a heart attack or under chronic stress from high blood pressure, the heart doesn’t just weaken. It physically reshapes itself in a process called remodeling. In the first 72 hours after a heart attack, the dead tissue thins and stretches as structural proteins between cells break down. This can cause the affected area to bulge outward, increasing strain on the remaining healthy muscle.
Over the following weeks and months, the dead muscle is replaced by scar tissue. Collagen becomes detectable within about a week and by 28 days has entirely replaced the lost heart cells. The problem is that scar tissue can’t contract. To compensate, surviving heart cells enlarge by as much as 70% in volume. The heart’s chambers gradually dilate and its shape distorts from a compact oval into something rounder and less efficient. This compensation works for a while, but over time the extra strain leads to further deterioration in pumping ability.
When the Heart Can’t Pump Enough Blood
Heart failure is what happens when these changes, or other conditions, leave the heart unable to circulate blood well enough to meet the body’s needs. It comes in two main forms. In one, the heart muscle is too weak to squeeze forcefully (reduced pumping strength). In the other, the muscle becomes too stiff to fill properly between beats, even though each squeeze is still relatively strong.
In the stiff-heart version, the ventricle loses its ability to pull blood in during the relaxation phase. Normally, the heart actively creates suction to draw blood from the upper chambers. When the muscle stiffens, filling depends on higher pressure pushing blood in instead. This backs pressure up into the lungs, causing breathlessness, and eventually into the veins throughout the body, causing swelling in the legs and abdomen. During exercise, the heart simply cannot increase its output enough, which is why fatigue and shortness of breath with activity are hallmark symptoms.
Electrical Problems That Disrupt Rhythm
Your heart relies on a precise electrical signal that starts at the top and travels downward, triggering the upper chambers to squeeze first and the lower chambers a fraction of a second later. This coordination ensures blood moves efficiently from chamber to chamber and out to your body.
Arrhythmias occur when these signals are generated abnormally, travel through the wrong pathways, or get delayed. In conditions like bundle branch block, one side of the heart contracts slightly out of sync with the other, reducing pumping efficiency. Atrial fibrillation, one of the most common rhythm disorders, causes the upper chambers to quiver chaotically instead of contracting in a coordinated way. Blood pools and moves sluggishly, which creates conditions for clots to form. If a clot travels to the brain, it causes a stroke.
Valve Problems That Overwork the Heart
The heart has four valves that open and close with each beat to keep blood flowing in one direction. Two things can go wrong: a valve can narrow (stenosis), forcing the heart to push harder to get blood through, or it can leak (regurgitation), allowing blood to flow backward. Either problem increases the heart’s workload.
With aortic valve stenosis, for example, the left ventricle has to generate significantly higher pressure than normal to force blood past the narrowed opening. Over time, this extra effort causes the heart wall to thicken. Eventually the muscle can’t keep up with the demand, and heart failure develops. Valve problems can result from aging, infection, or conditions present from birth.
Damage Beyond the Heart
Because the heart supplies blood to every organ, its decline creates a cascade of problems elsewhere. The kidneys are especially vulnerable. When the heart’s output drops, blood flow to the kidneys decreases, impairing their ability to filter waste and regulate fluid. This leads to fluid retention, which in turn increases blood volume, putting even more strain on the already struggling heart. It’s a vicious cycle that accelerates the decline of both organs.
The brain takes a significant hit as well. In a large review of heart failure patients, 43% showed measurable cognitive impairment. Reduced blood flow to the brain triggers oxidative stress, inflammation, and eventually the loss of neurons and their connections. People with coronary artery disease have a 27% higher risk of developing dementia compared to those without it. Atrial fibrillation raises the risk of cognitive impairment by about 39%, even in people who have never had a recognized stroke, likely because of tiny, silent clots that damage brain tissue without producing obvious symptoms. These silent brain infarcts are nearly three times more common in people with coronary heart disease.
Who It Affects Most
About 5% of adults over age 20 have coronary artery disease. While it’s often thought of as a disease of old age, one in six cardiovascular deaths in 2023 occurred in people younger than 65. The burden also falls unevenly across populations. Black Americans have the highest percentage of deaths attributed to heart disease at 22.6%, compared to 18.0% for white Americans and 11.9% for Hispanic Americans.
Heart disease is not a single event but a progressive condition. Arteries narrow over decades. The heart reshapes itself in response to injury. Organs downstream gradually lose function as blood supply diminishes. Each stage creates conditions that accelerate the next, which is why the damage compounds over time when risk factors like high blood pressure, high cholesterol, and diabetes go unmanaged.