According to a new study by cardiologists at UT Southwestern and Texas Health Resources. Exercise can reverse damage to sedentary, aging hearts and help prevent risk of future heart failure, if it's enough exercise, and if it's begun in time. This study published in Circulation.

To reap the most benefit, the exercise regimen should begin by late middle age (before age 65), when the heart apparently retains some plasticity and ability to remodel itself, according to the findings by researchers at the Institute for Exercise and Environmental Medicine (IEEM), which is a collaboration between UT Southwestern Medical Center and Texas Health Presbyterian Hospital Dallas.

The regimen included exercising four to five times a week, generally in 30-minute sessions, plus warmup and cool-down:

1. One of the weekly sessions included a high-intensity 30-minute workout, such as aerobic interval sessions in which heart rate tops 95 percent of peak rate for 4 minutes, with 3 minutes of recovery, repeated four times (a so-called "4 x 4").

2. Each interval session was followed by a recovery session performed at relatively low intensity.

3. One day's session lasted an hour and was of moderate intensity. (As a "prescription for life," Levine said this longer session could be a fun activity such as tennis, aerobic dancing, walking, or biking.)

4. One or two other sessions were performed each week at a moderate intensity, meaning the participant would break a sweat, be a little short of breath, but still be able to carry on a conversation — the "talk test." In the study, exercise sessions were individually prescribed based on exercise tests and heart rate monitoring.

At the end of the two-year study, those who had exercised showed an 18 percent improvement in their maximum oxygen intake during exercise and a more than 25 percent improvement in compliance, or elasticity, of the left ventricular muscle of the heart, Dr. Levine noted. He compared the change in the heart to a stretchy, new rubber band versus one that has gotten stiff sitting in a drawer.

In the current study, researchers wanted to know if exercise can restore the heart's elasticity in previously sedentary individuals – especially if begun in late middle age. Previous studies from Dr. Levine's research program have shown substantial improvements in cardiac compliance in young individuals after a year of training, but surprisingly little change if the training was started after age 65.

Researchers concluded that 53 participants, ages 45 to 64. Many came from the Dallas Heart Study, which includes 6,000 Dallas residents and is the only single-center heart study of its size and multiethnic composition. The Dallas Heart Study is designed to improve the diagnosis, prevention, and treatment of heart disease.