Diseases & Conditions : Transplantation
Anatomy and Function of the Heart Valves
What are heart valves?
The heart consists of four chambers, two atria (upper chambers) and two ventricles (lower chambers). Blood passes through a valve before leaving each chamber of the heart. The valves prevent the backward flow of blood. Valves are actually flaps (leaflets) that act as one-way inlets for blood coming into a ventricle and one-way outlets for blood leaving a ventricle. Normal valves have three flaps (leaflets), except the mitral valve, which only has two flaps. The four heart valves include:
Tricuspid valve. This valve is located between the right atrium and the right ventricle.
Pulmonary valve. The pulmonary valve is located between the right ventricle and the pulmonary artery.
Mitral valve. This valve is located between the left atrium and the left ventricle.
Aortic valve. The aortic valve is located between the left ventricle and the aorta.
How do the heart valves function?
As the heart muscle contracts and relaxes, the valves open and shut, letting blood flow into the ventricles and atria at alternate times. The following is a step-by-step description of how the valves function normally in the left ventricle:
When the left ventricle relaxes, the aortic valve closes and the mitral valve opens, to allow blood to flow from the left atrium into the left ventricle.
The left atrium contracts, allowing even more blood to flow into the left ventricle.
When the left ventricle contracts again, the mitral valve closes and the aortic valve opens, so blood flows into the aorta.
What is heart valve disease?
Heart valves can malfunction in several ways, including:
Regurgitation (or leakage of the valve). This means the valve doesn't close completely, causing the blood to flow backward through the valve. This results in leakage of blood back into the atria from the ventricles (in the case of the mitral and tricuspid valves) or leakage of blood back into the ventricles (in the case of the aortic and pulmonary valves).
Stenosis (or narrowing of the valve). With stenosis, the valve opening is narrowed or doesn't open properly, inhibiting the ability of the heart to pump blood across the narrowed valve due to the increased force required to pump blood through the stiff (stenotic) valve(s).
Atresia. This means the valve opening doesn't develop at all, preventing blood from passing from an atria to a ventricle, or from a ventricle to the pulmonary artery or aorta. Blood must find an alternate route, usually through another existing congenital (present at birth) defect such as an atrial septal defect or a ventricular septal defect.
When heart valves fail to open and close properly, the implications for the heart can be serious, possibly hampering the heart's ability to pump blood adequately through the body.