The heart valves are specialized structures that ensure one-way blood flow through the heart’s chambers. They open and close in response to pressure changes during the cardiac cycle (heartbeat).  
 
There are four main valves in the human heart — two atrioventricular (AV) valves and two semilunar valves. 
 
1. Atrioventricular (AV) Valves 
 
These valves separate the atria (upper chambers) from the ventricles (lower chambers). 
 
a. Tricuspid Valve 
Location: Between the right atrium and right ventricle. 
Structure: Has three cusps (flaps) made of thin connective tissue. 
Function: Opens when the right atrium contracts, allowing blood to flow into the right ventricle. Closes when the ventricle contracts (to eject blood) to prevent backflow into the atrium. 
 
Support Structures: 
Chordae tendineae: Tendon-like cords that attach the valve cusps to the papillary muscles in the ventricle wall. These prevent the valve from inverting (on itself) during contraction. 
 
b. Mitral (Bicuspid) Valve 
Location: Between the left atrium and left ventricle. 
Structure: Has two cusps. 
Function: Allows blood to flow from the left atrium to the left ventricle and prevents backflow when the ventricle contracts. 
Support: Also has chordae tendineae and papillary muscles for stability. 
 
2. Semilunar Valves 
 
These valves separate the ventricles from the major arteries leaving the heart. 
 
a. Pulmonary Valve 
Location: Between the right ventricle and the pulmonary artery. 
Structure: Has three crescent-shaped cusps (hence named “semilunar”). 
Function: Opens when the right ventricle contracts to allow blood into the pulmonary artery; closes to prevent blood from flowing back into the ventricle. 
 
b. Aortic Valve 
Location: Between the left ventricle and the aorta. 
Structure: Also has three semilunar cusps. 
Function: Opens during left ventricular contraction to let blood flow into the aorta; closes during relaxation to prevent backflow.