There are 2 valves in a sheep's heart. They are the mitral and tricuspid valve. The sheep also has a 4 chamber heart that is very similar to a human heart.

The valve

Mitral Valve

The valve between the heart and the aorta is the aortic valve, and the valve between the heart and the pulmonary artery is the pulmonic valve.

The aortic valve functions as a one-way valve between the heart and the rest of the body. Blood is pumped from the left ventricle of the heart, through the valve, and down the aorta, which in turn supplies blood to all of the organs in the body. Between heart contractions, the valve closes, preventing blood from flowing backwards into the heart. The function of the aortic valve is then twofold: (1) It provides a route for which blood can leave the heart, and (2) It prevents blood that has already left the heart from leaking backwards into the heart.