These circular orifices are located at the upper ends of the outflow parts of the left and right ventricles respectively. The pulmonary orifice which is 3 cms, is 0.5 cm larger than the aortic orifice. The aortic orifice is placed in front and to the right of the mitral orifice. The pulmonary orifice is placed above and to the left of the tricuspid orifice and the aortic orifice intervening between them. The pulmonary orifice is guarded by the pulmonary valve and the aortic orifice by the aortic valve. Each valve consists of three semilunar cusps. Each cusp is triangular. It has a convex edge which is attached to the part of the margin of the orifice. It has two free margins that meet at the apex of the cusp. Each cusp consists of a double fold of endocardium with some fibrous tissue in it. The region of the apex is thickened to form a nodule while crescentric parts near the free edges are called lunules.