Physical Exercise

Because the heart is a muscle, its performance improves with exercise. Regular exercise helps prevent heart attack and stroke by lowering blood pressure and low-density lipoprotein cholesterol (LDL, the bad kind). Exercise also makes blood vessel walls more flexible and, in turn, helps prevent hardening of the arteries and may help raise HDL cholesterol (the good kind.)

Reference:
Physical Activity and Health: A Report of the Surgeon General, Centers for Disease Control and Prevention, Nov. 17, 1999.