It declines by about 25 to 30 percent between ages 20 and 80, regardless of physical fitness status. The amount of oxygen used by the body at peak exercise capacity. Also known as VO2 max, it is considered the best measure of physical fitness. The valve between the left atrium and ventricle. It closes more slowly with age because the rate of blood flow into the left ventricle that pushes it closed decreases with age.
Myocardial infarction See heart attack.
The heart muscle. Myocyte A heart muscle cell. Myocytes decline in number but grow larger with age. A structure inside a cell, such as the sarcoplasmic reticulum. The amount of oxygen the entire body uses in a certain time period.