Just like the home you live in, I like to think of the heart as having plumbing, electricity, and carpentry. Most diseases of the heart can be traced to a problem in one of these systems. In other words, some heart diseases are due to plumbing problems, others to faulty wiring, and still others to the construction material itself.

A heart attack is caused by a problem in the plumbing. The blood vessels surrounding the heart, called coronary arteries, provide the heart with its very own blood supply, and that is priority one, since nothing can happen if the heart doesn’t have an adequate blood supply. So just as blood leaves the heart to enter the aorta, a tiny amount is immediately diverted into small arteries that feed the heart itself. Airline warnings that remind you to put on your own oxygen prior to assisting others are like an echo of the biological function of these tiny, essential coronary arteries. Just like air travelers, the heart must take its own oxygen first.

The largest coronary artery, the left main, is usually found in front, at the top of the left ventricle. A branch of the left main, the left anterior descending, continues down the front of the left ventricle. A smaller branch, the circumflex, wraps leftward toward the back. The right coronary artery feeds the right atrium and ventricle. The right side of the heart is smaller than the left, because it needs to pump blood only the short distance to the lungs.

What is a heart attack? A blockage in the coronary arteries. You could have a blockage in a distant part of a tiny branch of a coronary artery. Or you could be extremely unlucky and have a blockage in the left main, or left anterior descending arteries. Cardiologists call these “widow makers,” because they are likely to be disastrous. Have you ever held your arm up high in the air and felt the pain of a compromised blood supply? A heart attack hurts.

Who gets heart attacks? The risk of developing a blockage rises quickly with a number of known risk factors. These include diabetes, hypertension, obesity, high insulin levels, low HDL, high triglycerides, or large amounts of small, dense LDL. Add to these a sedentary lifestyle, and your risk of heart attack goes up fast. Risk factors are not additive, but rather multiplicative. That’s one reason being physically active is an important part of a prescription for reducing the risk of heart attack.

I’ll be honest — on my first day of medical school I could not have told you exactly what a heart attack was. I knew it was caused by some kind of blockage, but I didn’t know exactly where, how, or why. While the research continues to bring us closer to answers, let’s remember that it’s one thing for scientists to understand the basic physiology, and quite another for all of us to be able to talk about it together.

What else can go wrong in a heart? Problems in the electrical conduction system affect the timing of heart muscle contractions. Imagine for just an instant how important it is for the left atrium to contract before the left ventricle. An instant is about how much time your heart has to get this exactly right with each and every squeeze.

Problems in the “carpentry” can affect any heart structure, including the valves and muscles. The heart is a pump with two distinct phases: squeezing and relaxing. A swollen, floppy muscle makes it hard to squeeze properly. A stiff or shrunken muscle might make it hard both to squeeze and relax. Different kinds of problems affect the heart’s pumping ability in different ways, and they are treated with a variety of combinations of medicines, depending on the exact cause.

Illnesses of the heart can be congenital, meaning present from birth, or they can be acquired later, perhaps due to injury, or an infection, or exposure to a toxic chemical or even a vitamin deficiency. Some illnesses, like rheumatic heart disease, affect just a single structure (usually the mitral valve) while others, like longstanding alcohol abuse, can affect the entire heart muscle.

Lots can go wrong, but it usually doesn’t. And lots can be repaired, even if it goes off track temporarily. Continuing to nourish yourself, moving regularly, and relaxing your mind and body will improve the odds that your heart will keep ticking just the way it’s meant to.