A primary goal of physical exercise is often to improve the strength of the heart muscle itself. The heart can grow stronger through regular, sustained periods of increased effort. This conditioning is possible during exercise, because the heart must then beat harder and faster to pump sufficient blood to the active muscles, and to deliver adequate oxygen to the lungs. However, the safest and most effective cardiovascular (kar-dee-o-VASK-you-lar) conditioning usually occurs when the heart rate increase is limited to a specific range. This range, called the target heart rate, is generally considered to be from 50 to 75 percent of a person's maximum heart rate. Usually, maximum heart rate or MHR (M-H-R) is figured by subtracting the individual's age from 220. The target range is quite specific to each individual, varying with age, physical fitness level, and overall general health. One simple method for calculating this range involves determining the person's maximum heart rate, then multiplying that number by both 50 percent and 75 percent. With these two numbers in mind, the heart rate can be measured at the beginning, middle and end of the activity, and compared to the appropriate range. If the exercise does not increase the heart rate to within this range, a harder workout may be necessary to benefit the heart muscle. If the activity increased the rate above the target range, a less intense workout may be advisable. After six months of continuous regular exercise that brings the heart to its target rate, the high end of the range may be extended to 85 percent of MHR, with the approval of a healthcare provider. People with other health conditions such as pregnancy, existing cardiovascular disease, or high blood pressure usually require a different calculation for their individual safe target heart rate. If you're interested in finding out more about your individual target heart rate, or have questions about starting an exercise program, contact a healthcare provider.