Everyone knows that to stay healthy you must eat right and exercise. But what kind of exercise gives you the most benefits? Should you focus on cardio exercises or strength training to boost heart health?

"Everybody is focused on heart rate, heart rate" says Chauncey Crandall, M.D., the New York Times bestselling author and director of preventive medicine at the Palm Beach Cardiovascular Clinic in Florida.

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"But I like to focus on endurance," Dr. Crandall tells "Newsline."

In the past, it was thought that cranking up the heart rate as high as it would go was the way to achieve the best workout. But while heart rate is important, significantly elevating heart rate during exercise is not as important as once thought. "All the medical information tells us that endurance is the key," says Crandall.

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Crandall says that working out for one hour every day, at least five days a week, is the best workout you can do. "A continuous workout from beginning to end," stresses Crandall, author of "The Simple Heart Cure: The 90-Day Program to Stop and Reverse Heart Disease" and editor of the popular "Dr. Crandall's Heart Health Report" newsletter.

Focusing on heart rate isn't needed unless your heart rate is abnormal, says Crandall. An abnormal heart rate would be a persistent heart rate that is above 100 beats per minute. Below 60 or 50 beats per minute are also abnormal, says Crandall.

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As we age, our heart rate changes. For example, some older people need a pacemaker because their heart rates become too slow, Crandall explains.

The good news is we have all these devices now to record your heart rate, says Crandall. Apple Watch is one, and there are monitors you can buy on Amazon, says Crandall.