Regular exercise and increased aerobic fitness are widely recommended by the American Heart Association, and for good reasons.

Moderate-to-vigorous physical activity improves the risk factor profile for heart disease, reduces the likelihood of inappropriate blood clotting, and, through autonomic nervous system adaptations, decreases the likelihood of inadequate blood flow to the heart muscle (ischemia) and threatening heart rhythm irregularities. Moreover, higher levels of aerobic fitness are strongly associated with a lower overall risk of acute cardiac events.

But it provides another and somewhat surprising benefit: Leisure-time or recreational physical activity can help you survive a heart attack.

What is preconditioning?

Decades ago, researchers found that regularly exercised dog hearts could be rendered largely resilient to major heart damage or life-threatening heart rhythm irregularities after experimentally-induced heart attacks. Now, studies confirm that exercise preconditions the human heart in a similar way. A recent investigation of nearly 2,200 patients hospitalized for heart issues found that preadmission physical activity habits reduced in-hospital death rates and improved cardiovascular outcomes one month after hospital discharge, even after adjusting for related outcome determinants.

Just one to three sessions of moderate-intensity physical activity corresponding to perceived exertion ratings of “somewhat hard,” lasting from 20 to 30 minutes, provides cardioprotective effects that persist for several days to more than a week after the last exercise session. Although the mechanisms responsible for the immediate cardioprotective benefits of the prior exercise remain unclear, researchers believe it may be due to transiently altered biochemical pathways or enhanced cardiac electrical stability. While moderate-intensity exercise provides robust protection against heart attacks, higher-intensity exercise does not bolster the magnitude of protection.

Practical implications

Anyone with known or suspected heart disease should engage in multiple weekly bouts of exercise. If you don’t think you have underlying heart disease, think again. Studies from the Cleveland Clinic suggest that approximately 85 percent of all Americans over the age of 50 have underlying atherosclerotic cardiovascular disease. Even if you’re under 50, the American Heart Association recommends getting a total of 150 minutes of moderate physical activity over the course of the week.

Estimating moderate activity

What constitutes moderate activity differs for each person and depends largely on your current fitness level.

Talk test. A quick way to estimate your exercise intensity is the talk test. At moderate intensity, you should be breathing harder than normal, but still be able to converse in brief sentences. If you can’t say more than a few words without having to catch your breath, you’ve crossed into vigorous activity.

Heart rate. You can also monitor your heart rate to estimate your workload. First, calculate your maximum heart rate (MHR) by subtracting your age from 220. Multiply your MHR by 0.5 and then by 0.7. That is the American Heart Association’s recommended target range for moderate activity: 50 to 70 percent of maximum work. Wearing a heart rate monitor is an easy way to track your heart rate as you exercise, but you can also periodically check your pulse.

Whether you invest 20 minutes each day or an hour a few days a week, activities like brisk walking, water aerobics, dancing, biking, or playing doubles tennis can provide valuable heart benefits.