Good news! You don't have to run miles every day to have a healthy heart. A brisk walk around the park or on the treadmill is likely enough exercise to keep your heart strong, according to a study from the Duke University Medical Center.

Specifically, you need to walk at a fast pace for two to three hours each week, which translates to 30 to 45 minutes most days of the week, to significantly cut your risk of cardiovascular disease, reports The Associated Press. This supports earlier research that reached a similar conclusion. "The classic question always is: What's the minimum amount I need to do to enjoy the benefits of it?" lead study author Brian Duscha told AP. "If you just walk 12 miles a week at a brisk pace, it's scientifically proven now that you will get some benefits."

The study: More than 130 middle-aged and overweight sedentary men and women who were at risk for heart disease participated in the study. Each was placed in one of these four groups:

• No exercise.
• Walk briskly for 12 miles a week at moderate intensity.
• Walk briskly or jog slowly 12 miles a week at a vigorous intensity.
• Jog 20 miles a week at a vigorous intensity.

The results: Participants in all three groups who exercised saw fitness improvements. Walking briskly at either a moderate intensity or vigorous intensity provided similar levels of peak oxygen consumption. (Those who jogged had even higher oxygen consumption, so more exercise is better.)

If you exercise and don't lose weight, don't despair. Duscha says that as we age, we gain about 4 pounds a year if we maintain the same diet and don't exercise. So if you're maintaining your weight year-after-year in middle age, congratulate yourself!

The study findings were published in the journal Chest.