The ventricles. The right and left ventricles are separated by inter ventricular septum. The septum slopes obliquely with convexity towards the right ventricle. The left ventricle is longer and more conical than the right, and forms the apex of the heart. The left ventricle shows the following important features:

1. The left atrio-ventricular opening guarded by a mitral or bicuspid valve.

2. A circular opening of the aorta guarded by aortic or semilunar valves. The valves allow the blood to enter the aorta from left ventricle during ventricular contraction and prevents it from flowing back into the ventricle during relaxation. The aortic valve has 3 cups-two posterior (right and left) and one anterior.

3. The trabeculae carneae (chordae tendinae), are attached to the margins of the bicuspid valve and prevent them from everting into the atrium.

4. The papillary muscles, two in number, to which one end of the chordae tendinae is attached .

The right ventricle has :

1. Right atrio-ventricular opening guarded by the tricuspid valve.

2. A rounded opening of the pulmonary artery, guarded by semilunar valves. The semilunar valves prevent backflow of the blood.

3. The trabeculae carneae are as in the left ventricle, but they are not as stout and strong.

4. The papillary muscles are conical in shape with their bases attached to the walls of the ventricle and their apices directed towards the ventricular cavity.