Between the atria and ventricles are valves (AV or atrioventricular valves). Semilunar valves are between the ventricles and the major arteries leaving the heart. The tricuspid valve separates the right atrium from the right ventricle. The mitral (bicuspid) valve separates the left atrium from the left ventricle. These valves are set in fibrous rings that provide the site of the origin and insertion of the myocardium. The valve between the right ventricle and pulmonary trunk is the pulmonary (semilunar) valve. The valve between the left ventricle and aorta is the aortic (semilunar) valve.
One-way valves ensure that blood flow is in one direction. Chordae tendineae are strong, tendon-like cords attached to the leaflets (cusps) of the atrioventricular valves. The chordae tendineae prevent the AV valves from inverting when the ventricles contract. Papillary muscles attached to the chordae tendineae contract with the ventricles to prevent back-flow into the atria.
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