Few things in life make an otherwise healthy person feel more fragile than a diagnosis of heart disease. Even without having had a heart attack, the sober announcement by your family doctor that you have heart disease is usually a deeply unnerving event. Suddenly, you feel quite vulnerable.

Instinct may tell you the best and safest thing to do is go home, lie down, and have a good long rest. Let the heart repair itself. For decades, doctors had the same instinct. They often kept patients at rest in the hospital or at home for weeks. But researchers have discovered this instinct was wrong: exercise is good for the heart.

It may be most important for people who have heart disease. Studies show that, in people with heart disease, exercise-based rehabilitation strengthens the heart and helps it to work more efficiently. In fact, for people with heart disease, doing exercise as part of a rehabilitation program is associated with a 25 percent lower risk of having a fatal heart attack or stroke.

Why? Because exercise doesn’t just strengthen the heart muscle itself; it improves the health of your arteries and the rest of your cardiovascular system, too. In the process it reduces the likelihood that clots will form that might trigger a heart attack. Exercise lowers blood pressure and increases HDL (good) cholesterol levels, keeps blood sugar under control, and increases overall endurance.

It is true that people who exercise sometimes have heart problems, but this occurs far less frequently than it does in people who don’t exercise. What’s more, research demonstrates that participating in an exercise program even after a heart attack may lower your chances of dying from a heart problem by 20 to 30 percent.

A study of 21,000 people has shown that men who exercised enough to work up a sweat at least once a week were 20 percent less likely to have a stroke. A study of women found that walking briskly at least three hours a week cut their risk of heart disease by 30 to 40 percent.

Indeed, exercise even fights the depression that often follows a heart disease diagnosis or a heart attack. After all, it’s hard to keep thinking of yourself as fragile when you’re working up a sweat. Does that mean the first thing you should do after your diagnosis is start vigorous exercise?

Of course not. But guided by your doctor and an exercise professional, exercise is not only safe, it’s critical to your long-term health. With a little imagination, it can even be fun—a lot more fun than another heart attack.

What the Guidelines?

Health organizations like the Centers for Disease Control and Prevention and the National Institutes of Health now recommend that adults exercise at least 30 minutes every day.

The Institute of Medicine, an authoritative group of medical experts, recently went even further: it recommends that all adults engage in at least 60 minutes of moderately intense physical activity most days of the week in order to maintain ideal body weight and gain all the other benefits that come with being active.

For those who can’t meet these goals, however, the advice of all the experts is simple: “Some exercise is better than none, and more is better than some.” These recommendations are not specifically for patients with heart disease, and they indicate a growing enthusiasm for encouraging physical activity.

The American Heart Association/American College of Cardiology guidelines recommend that people with heart disease do at least 30 minutes of aerobic exercise daily, or at a minimum three to four times a week. Aerobic (which means “oxygen demanding”) exercise works large muscle groups in your body continuously over a period of time at a level vigorous enough to raise your heart rate.

How you achieve this goal is up to you, with the guidance of your doctor. What’s important is that you find a form of exercise, or combination of exercises, that you will want to keep up. Sure, joining a gym and working out on a treadmill, stair climber, or any of the many other aerobic exercise machines currently available will work.

But so will dancing, bicycling, even walking, so long as you do it briskly and often enough. And that’s not all. The guidelines also recommend that in addition to working out, you modify your lifestyle in a way that makes your daily routine more active.

For some heart disease patients this means skipping the coffee break and taking a walking break instead. Or taking the stairs instead of the elevator. Or being more actively involved in gardening. How you do it is up to you; what matters is that you do it.

Why Exercise Matters

The human body, and the heart that keeps it alive, were made for work. From the Stone Age until roughly fifty years ago, hard physical work was the norm for most people, as it still is today in many parts of the world where, in fact, heart disease is much less common.

But during the twentieth century, as industrial societies became more technologically advanced, our lives became more sedentary. We went from hand scythes to push mowers, and from push mowers to power mowers, from power mowers to riding mowers, to pick just one example. As we become more sedentary, we become more disease-and injury-prone.

Muscles weaken. Weight piles on. Joints stiffen. Bone density decreases. The risk of disease—colon cancer, diabetes, anxiety, depression, and many more—increases sharply. At the top of the list is America’s number-one killer, heart disease, and related conditions like high blood pressure and stroke.

In short, our comfortable lives are killing us. Many people don’t exercise regularly. More than half of all Americans don’t. Many don’t exercise at all. We find lots of reasons not to exert ourselves. We don’t have the time. Or the money. Or the equipment. But mostly, we don’t have the will.

In a society busily inventing new conveniences, it’s increasingly easy to avoid physical work. We don’t even have to leave the couch to change channels on our televisions. Our bodies may be designed for hard work, but, like pieces of equipment, if left idle too long they fall into disrepair.

Fortunately, it’s almost never too late to start working your heart. Stated simply: the more exercise you get—even if it’s only walking regularly—the lower your chance of having heart problems and the better your chance of beating them if you do. And if you have been exercising, then the goal is to get you back to your high level of activity—or more.