Right Ventricle
Blood from the right atrium passes through the right atrioventricular (AV) valve (also called the tricuspid valve) to fill the right ventricle. The right AV valve is characterized by three valve leaflets, or cusps. Each cusp is held in position by strong tendinous cords called chordae tendineae . The chordae tendineae are secured to the ventricular wall by cone-shaped papillary muscles. These structures prevent the valves from everting, like an umbrella in a strong wind, when the ventricles contract and the ventricular pressure increases.
Ventricular contraction causes the right AV valve to close and the blood to leave the right ventricle through the pulmonary trunk and to enter the capillaries of the lungs via the right and left pulmonary arteries. The pulmonary valve (also called the pulmonary semilunar valve) lies at the base of the pulmonary trunk, where it prevents the backflow of ejected blood into the right ventricle.
Left Atrium
After gas exchange has occurred within the capillaries of the lungs, oxygenated blood is transported to the left atrium through two right and two left pulmonary veins.
Left Ventricle
The left ventricle receives blood from the left atrium. These two chambers are separated by the left atrioventricular (AV) valve (also called the bicuspid valve or mitral valve). When the left ventricle is relaxed, the valve is open, allowing blood to flow from the atrium into the ventricle; when the left ventricle contracts, the valve closes. Closing of the valve during ventricular contraction prevents the backflow of blood into the atrium.
The walls of the left ventricle are thicker than those of the right ventricle because the left ventricle bears a greater workload, pumping blood through the entire body. The endocardium of both ventricles is characterized by distinct ridges called trabeculae carneae . Oxygenated blood leaves the left ventricle through the ascending portion of the aorta. The aortic valve (also called the aortic semilunar valve), located at the base of the ascending portion of the aorta, closes as a result of the pressure of the blood when the left ventricle relaxes, and thus prevents the backflow of blood into the relaxed ventricle.