No discussion of the circulatory system would be complete without mentioning some of the problems that can occur.

As mentioned earlier, several problems can occur with the valves of the heart.

Valvular stenosis is the result of diseases such as rheumatic fever, which causes the opening through the valve to become so narrow that blood can flow through only with difficulty. The result can be blood damming up behind the valve.

Valvular regurgitation occurs when the valves become so worn that they cannot close completely, and blood flows back into the atria or the ventricles. If the blood can flow backward, the efficiency of the cardiac stroke is drastically reduced.

Vascular Problems The coronary arteries are also subject to problems. Atherosclerosis is a degenerative disease that results in narrowing of the coronary arteries.

This is caused by fatty deposits, most notably cholesterol, on the interior walls of the coronary arteries. When the walls become narrowed or occluded, they reduce the blood flow to the heart muscle.

If the artery remains open to some degree, the reduced blood flow is noticed when the heart is under stress during periods of rapid heartbeat. The resulting pain is called angina. When the artery is completely closed or occluded, a section of the heart muscle can no longer get oxygenated blood, and begins to die.

This is called a heart attack. Only quickly restoring the blood flow can reduce the amount of heart muscle that will die.

At times, the walls of the systemic arteries become weakened. When this occurs, the wall may balloon outward, much like a weak spot in the radiator hose.  This called an aneurysm, and is an extremely dangerous condition. Like a radiator hose under pressure, the wall can rupture.

Blood can then spill out of the circulatory system into the body cavity. If an aneurysm ruptures in the aorta, death is almost certain.