There is a gradual accumulation of insoluble granular material (lipofuscin, or “age pigment”) in cardiac muscle fibres.
These granules, composed of protein and lipid (fat), make their first appearance by the age of 20 and increase gradually, so that by the age of 80 they may occupy as much as 5–10 percent of the volume of a muscle fibre.
The biological-physiological aspects of aging include both the basic biological factors that underlie aging and the general health status.
This reduction in power, or rate of work, is due to the age-associated reduction in the activities of certain cellular enzymes that produce the energy required for muscular contraction.
In spite of these changes, the heart, in the absence of disease, is able to meet the demands placed upon it.
In response to physical exercise it can increase its rate to double or triple the amount of blood pumped each minute, although the maximum possible output falls, and the reserve capacity of the heart diminishes with age. It is a progressive disorder and is present to some extent in practically all individuals by middle life.
Arteriosclerosis, or hardening of the arteries, increases markedly in incidence with age, and is often regarded as part of aging. It is, therefore, impossible to make a clear distinction between the effects of aging and the effects of disease in blood vessels in human beings.
Under resting conditions, the heart rate does not change significantly with age.