The heart isn't the only muscle to benefit from regular exercise. Most of the other muscles in your body enjoy exercise, too. When you use your muscles and they become stronger, it allows you to be active for longer periods of time without getting worn out.
Strong muscles are also a plus because they actually help protect you when you exercise by supporting your joints and helping to prevent injuries. Muscle also burns more energy when a person's at rest than fat does, so building your muscles will help you burn more calories and maintain a healthy weight.