If you’ve been a couch potato most of your life, there is still hope for your heart. Years of inactivity, along with aging, can lead to a weakened heart, but revving up your activity level can reverse the damage and improve heart health.

Middle age people who are sedentary and unfit often have small, stiff chambers in the left ventricle of the heart, leaving it unable to pump blood as effectively as someone in that age range who was more active. In comparison, the heart chambers of people who exercised regularly over the course of their lives remained large and elastic.

People in the exercise group had an 18 percent improvement in their maximum oxygen intake while exercising, and the elasticity of the left ventricular muscle of the heart improved by 25 percent.

It's like the difference between a new rubber band and one that has been left sitting in a drawer and gotten stiff over time, Benjamin Levine, lead researcher on a recent study and Professor of Internal Medicine at University of Texas Southwestern, explained.

The team wanted to see if couch potatoes could restore their hearts' elasticity with exercise. They divided 50 people into two groups. One group received supervised exercise training for two years while the other group participated in yoga and balance training.

Those in the exercise group took part in four to five exercise sessions per week. These included one high-intensity, 30-minute workout performed in intervals; two to three hour-long sessions of an activity of moderate intensity like playing tennis or riding a bike; and one or two strength training sessions using weights or machines.

They did not begin at this level of exercise, of course. It took three months to reach high-intensity aerobic interval training after starting with three, 30-minute, moderate-level activities.

After two years, the people in the exercise group had an 18 percent improvement in their maximum oxygen intake while exercising. The elasticity of the left ventricular muscle of the heart improved by 25 percent.

To get the most benefit, such an exercise program is best begun before the age of 65, while the heart still has some plasticity and can heal itself, the researchers say; and exercising two to three times a week is not enough. You really need to make your heart muscle work. As with any exercise program, gear up slowly, so you don't injure yourself. Consulting with your doctor is probably the best place to start if you are not in shape.

“When the muscle stiffens, you get high pressure and the heart chamber doesn't fill as well with blood. In its most severe form, blood can back up into the lungs. That's when heart failure develops,” Dr. Levine explained.

So check out your local recreation center. Connect with a walking group. Get a bike and use it daily. Take up a sport. Join a gym, or relive your youth and put on your dancing shoes.

The study is published in Circulation.