The primary reason for angina is the flow of lesser-than-usual blood to the
heart muscle. To remain alive, the heart muscle needs oxygen which comes
from the blood. An insufficient flow of blood to the heart muscle means an
inadequate supply of oxygen to it which elevates the risk of ischemia.
In most cases, it is coronary heart disease that prevents the flow of blood to
the heart muscle. By causing the formation of plaques, it narrows arteries and
restricts the flow of blood to the heart muscle. In medical terms, this condition
is known as atherosclerosis.
Narrow arteries elevate the risk of reduced blood flow to the heart muscle in
two ways. It can either happen due to the bursting of plaques in a narrow
artery or due to the formation of blood clots in it.
The effect of angina is more readily visible after an activity than during a
resting phase. This is because when you take rest, the heart muscle works
even with the reduced supply of oxygen. But the cells of the body, including
that of the heart muscle, demand more oxygen after a heavy activity such as a
workout. As a result, there is a higher likelihood of the symptoms of angina
becoming more visible.