On my first day of medical school I could not have told you exactly what a heart attack was. I knew it was related to some kind of blockage, but I didn’t know exactly how, where, or why. And though I’m not sure whether anyone yet can explain exactly why, the research continues to bring us closer to answers. At a certain point though, I did begin to understand what heart attacks are, and that is what I’d like to discuss today. 

The heart is a house with four rooms. Two ante-rooms, the right atrium and left atrium (pl. atria), act as entryways; the other two rooms, the right and left ventricles, are the main rooms. Blood begins its journey through the heart by entering the right atrium, after which it moves through the tricuspid valve to the right ventricle. It is then pumped to the lungs, where it receives oxygen. After this brief interlude, the blood returns to the heart, this time into the left atrium. It passes through the mitral valve to the left ventricle (the largest room), after which it is pumped into the aorta (the largest blood vessel in the human body), to bring oxygenated blood to the entire body.

Think of the heart as having plumbing, electricity, and carpentry. Diseases of the heart can usually be traced back to a problem in one or more of these systems. In other words, some heart problems are due to plumbing issues, others to faulty wiring, and still others to either the material itself, or how it is constructed.

Heart attacks happen in the plumbing. Blood vessels surround the heart to provide it with its very own blood supply. If blood cannot flow easily through those vessels, the heart muscle will not receive the oxygen it needs to function.  

At the same time that blood leaves the left ventricle and enters the aorta, a small amount is diverted into small arteries that feed the heart itself. These small arteries are called the coronary arteries. The word coronary means heart. This efficient system reminds me of an airline’s warning to passengers that they put on their own oxygen prior to assisting those around them. The heart is designed to take blood for itself first. 

Usually, the largest coronary artery, called the left main, heads toward the front of the left ventricle. The left main has a large branch, called the left anterior descending, that goes straight down the left ventricle. A smaller branch, the circumflex, wraps leftward around to the back. A second coronary artery is called the right coronary artery. It feeds the right atrium and ventricle, which are smaller than their left-sided counterparts because they pump their blood only to the lungs. The lungs are much closer and comparatively easy to reach than the rest of the body, whose blood is supplied by the large left ventricle. 

A heart attack is a blockage in the coronary arteries. You could have a heart attack in one of the last tiny branches of the coronary arteries. Or you could be extremely unlucky and have a heart attack in the left main or left anterior descending arteries. These are the blockages that cardiologists refer to as widow makers. These are more likely to be disastrous, as they supply blood to such a large sector of heart muscle. Think how painful it quickly becomes when you raise your arm up high in the air and deprive it of its blood supply. This is why a heart attack hurts so much.  

The likelihood of developing a blockage rises dramatically if you have diabetes, hypertension, obesity, high insulin levels, low HDL, high triglycerides, or large amounts of small, dense LDL. As well as a sedentary lifestyle. Being physically active markedly reduces the likelihood of developing a blockage. 

What other kinds of heart disease are there? Problems in the electrical conduction system affect the timing of heart muscle contractions. Consider, for an instant, how important it is for the atria to contract before the ventricles. An instant is about how much time your heart has to get this exactly right every time it contracts. 

Problems in the carpentry might affect the valves or anatomy of the heart, a specialized pump made mostly from muscle. Pumping has two phases, squeezing and relaxing. If the muscle becomes enlarged and floppy, it becomes hard to squeeze. Or it can become stiff and shrunken, which makes it hard to relax. Both problems affect the heart’s ability to pump efficiently, and these abnormalities are treated with different medicines, depending on the exact problem.

Illnesses of the heart can be congenital, meaning that you are born with them, or they can be caused by an injury, whether biological (e.g., viral, bacterial) or chemical (e.g., vitamin deficiency, exposure to toxins, e.g., excessive alcohol). Illnesses can affect a single area, like rheumatic heart disease, which preferentially damages the mitral valve; or they can affect the entire heart muscle.