Cholesterol seems to have taken on a life of its own in today’s society. People brag about their levels or bemoan them, but often without any real understanding of the role cholesterol plays in causing heart disease.

Some people expend enormous emotional energy worrying about their cholesterol levels, while ignoring other issues that play an equally important role in causing the coronary arteries to be blocked. In most people, cholesterol is only one factor—though a very important one—in the complex process that leads to atherosclerotic heart disease.

And atherosclerotic heart disease has been the number one killer of Americans every year since 1921. Lowering your blood cholesterol is one of the five basic health-care steps that will keep you from becoming a heart disease statistic, along with not smoking, eating right, exercising, and controlling your blood pressure.

Your heart muscle (myocardium) is about the size of your clenched fist. It sits behind the breastbone and beats constantly, starting shortly after conception and continuing for more than seventy years in most Americans.

Although it was once thought to be the seat of the soul, the heart is really a remarkable pump: it pumps oxygenated blood to all the cells in the human body, including its own cells, bringing them needed nourishment and hormones, and it sends the used or deoxygenated blood back to the lungs so the cycle can begin again.

The major artery that delivers blood from the heart to the rest of the body is called the aorta. The aorta has two branch arteries, the right and left coronary arteries, which bring blood to the heart. These two arteries each branch into progressively smaller and smaller channels.

The left coronary artery typically splits into two large branches that are responsible for supplying nutrients to the cardiac muscle that drives blood throughout the body. Coronary artery disease (CAD) begins with a buildup of plaque in either the left or right coronary artery or their branches.

This reduces the blood flow to the heart, but early on, this reduction is not severe enough to compromise heart muscle function or to produce any symptoms. Later, as the plaque enlarges and further reduces blood flow, blood flow interruption can reach the critical point where the heart muscle no longer gets adequate oxygen delivery when it is working vigorously (as when you exercise).

Ischemia is the medical word for this interruption. A temporary or partial interruption in the supply of blood, known as mild ischemia, will injure the myocardium and cause the chest pain known as angina. A prolonged or complete interruption, known as severe ischemia, will kill myocardial cells and cause a heart attack.

You can think of a coronary blockage as a car accident that blocks the flow of traffic through one of a handful of roads that serve a very important city. The more neighborhoods served by a road, the more disruptive a blockage is to the life of the city.

Generally, the more heart muscle a coronary artery feeds, the more devastating its failure is to the heart. There are exceptions to this rule. For example, a relatively minor blockage can set off extreme electrical instability in the heart that can prove fatal because the heart muscle can no longer contract in a coordinated fashion.

If the function of the electrical circuits could be restored in a timely fashion, through the use of drugs or a defibrillator, this injury might not even result in a detectable loss in muscle-pumping power. Heart-shocking devices called defibrillators were once available only in hospitals and ambulances, but they’re now popping up in public places.

You can find these public versions, called automated external defibrillators, in airports, movie theaters, fitness centers, casinos, malls, office buildings, and elsewhere. They are so easy to use that sixth graders who have never seen one before can master them in a minute or so.

The machines have easy-tounderstand instructions on them, and it’s basically just a matter of turning on the machine, attaching the pads to the victim’s bare chest—one on the upper part of the person’s right chest and the other on the left side near the armpit—waiting for the machine to analyze the heart rhythm, and pressing the shock or rescue button if the machine tells you to do so. Using these machines could save a life, as can performing cardiac resuscitation methods like CPR.