Coronary arteries are the blood vessels that supply oxygen-rich blood directly to your heart muscle. Though the heart pumps blood to every organ in your body, it can’t nourish itself from the blood passing through its chambers. Instead, it relies on a dedicated network of arteries that wrap around its outer surface, delivering the fuel the heart needs to keep beating. When these arteries narrow or become blocked, the result is coronary artery disease, the most common form of heart disease in the United States, responsible for over 371,000 deaths in 2022 alone.
The Four Major Coronary Arteries
Two main coronary arteries branch off the aorta, the large vessel that carries blood out of the heart. From there, they divide into smaller branches that cover different regions of the heart.
The left main coronary artery is short but critical. It quickly splits into two major branches:
- Left anterior descending artery (LAD): Runs down the front of the heart and supplies blood to the front of the left ventricle, the heart’s main pumping chamber. It also feeds the septum, the muscular wall dividing the left and right sides.
- Left circumflex artery: Wraps around the left side of the heart, delivering blood to the outer wall and back of the left ventricle.
The right coronary artery (RCA) supplies the right side of the heart, including the right ventricle and right atrium. It also feeds the electrical nodes that control your heartbeat, the SA node (your heart’s natural pacemaker) and the AV node (which coordinates signals between the upper and lower chambers).
In about 70% to 80% of people, the right coronary artery also gives rise to a branch called the posterior descending artery, which supplies the bottom wall of the heart. This pattern is called “right dominance.” Around 5% to 10% of people are left-dominant, meaning that branch comes from the left circumflex artery instead. The remaining 10% to 20% have a codominant pattern where both sides contribute.
How Coronary Arteries Feed the Heart
Your coronary arteries have an unusual challenge: the heart muscle they supply is constantly squeezing. During each contraction (systole), the heart compresses its own blood vessels, reducing flow. Most of the blood delivery to the heart muscle actually happens between beats, during the relaxation phase called diastole. This is when the ventricles fill with blood and the coronary arteries experience their peak flow. It’s also the only time blood can reach the innermost layer of the heart wall, which sits farthest from the arterial supply.
This timing matters. Anything that shortens the relaxation phase, like a very fast heart rate, reduces the window for coronary blood flow. That’s one reason a racing heart during exercise can trigger symptoms in someone whose arteries are already partially blocked.
How Coronary Arteries Become Blocked
Coronary artery disease develops through a process called atherosclerosis, which unfolds over years or even decades. It starts when the inner lining of an artery becomes damaged, often from high blood pressure, smoking, high cholesterol, or chronic inflammation. Once that lining is compromised, cholesterol particles (specifically LDL, the “bad” cholesterol) slip beneath the surface and become trapped.
Once stuck in the artery wall, those LDL particles undergo chemical changes. The body’s immune cells, called macrophages, rush in to clean up the modified cholesterol. But as they absorb more and more of it, they become bloated “foam cells” that can’t leave. This buildup of foam cells creates what’s known as a fatty streak, the earliest visible sign of atherosclerosis.
Over time, the fatty streak grows into a more complex plaque. Dead foam cells and accumulated fats form a soft, unstable core. The body tries to contain this by building a fibrous cap over the top, made of collagen and smooth muscle cells that migrate from deeper layers of the artery wall. Initially, the artery compensates by expanding outward to preserve blood flow. But eventually this remodeling fails, and the plaque begins to encroach on the open channel where blood flows.
The danger isn’t always from gradual narrowing. If the fibrous cap tears or ruptures, it exposes the plaque’s contents to the bloodstream, triggering a blood clot that can suddenly block the artery. This is how most heart attacks happen.
Symptoms of Reduced Coronary Blood Flow
When a coronary artery narrows enough to restrict blood flow, the heart muscle it supplies doesn’t get enough oxygen. The most recognizable symptom is angina, a pressure or tightness in the chest that some people describe as feeling like someone is standing on their chest. It typically shows up during physical activity or emotional stress and eases with rest.
Chest pain isn’t the only signal. Shortness of breath and extreme fatigue during routine activities can develop when the heart can’t pump efficiently because part of its muscle is starved for oxygen. Some people, particularly women and people with diabetes, experience less obvious symptoms like jaw pain, nausea, or back discomfort instead of classic chest pressure. If an artery becomes completely blocked, the result is a heart attack, where heart muscle begins to die within minutes.
About 1 in 20 adults age 20 and older in the U.S. have coronary artery disease. Many don’t know it until symptoms appear, because significant plaque buildup can exist for years without causing noticeable problems.
How Coronary Artery Problems Are Diagnosed
Diagnosis starts with your symptoms, medical history, family history, and risk factors. From there, several tests can evaluate how well your coronary arteries are working:
- Stress tests monitor your heart while it works hard, using an ECG or imaging to check for areas that aren’t getting enough blood flow.
- Coronary calcium scans measure calcium deposits in artery walls, which signal the presence of plaque. This is a quick CT scan that doesn’t require dye or needles.
- CT angiography uses contrast dye and a specialized X-ray machine to produce detailed images of the coronary arteries and identify blockages.
- Invasive coronary angiography threads a thin catheter to the heart and injects dye directly into the coronary arteries. This is the most precise method and can be combined with treatment in the same procedure.
Additional tools like cardiac MRI and PET scans can assess blood flow through the coronary arteries and detect areas of heart muscle that have been damaged by poor circulation.
Treatment When Arteries Are Blocked
Treatment depends on how severe the blockages are, how many arteries are affected, and your overall health. For mild to moderate disease, medications to lower cholesterol, control blood pressure, and prevent clotting are often the first approach, alongside lifestyle changes like diet, exercise, and quitting smoking.
When blockages are more severe, two main procedures can restore blood flow. Stenting involves threading a small balloon-tipped catheter to the blockage, inflating it to open the artery, and placing a tiny mesh tube (stent) to hold it open. Recovery is relatively quick since there’s no major surgery involved, and it works well for simpler blockages in one or two arteries.
Bypass surgery reroutes blood around blocked sections using a healthy blood vessel grafted from another part of the body, typically the chest wall or leg. It’s a more involved operation with a longer recovery, but it tends to produce better long-term results for people with complex blockages in multiple arteries, severe disease in the left main artery, or diabetes. The choice between stenting and bypass hinges on the specific anatomy of the blockages, the number of arteries involved, and individual risk factors like age and heart function.