Then heart consists of four chambers; 2 atria and 2 ventricles. These four chambers are:

1. Right atrium

The right atrium is the entrance to the heart and receives blood with low or no oxygen from the superior and inferior vena cava veins and also from the lungs through the pulmonary veins. An electrical impulse causes the muscles of the right atrium to perform wave-like contractions. The tricuspid valve which separates the right atrium from the right ventricle opens to let the de-oxygenated blood flow into the right ventricle. When the tricuspid valve closes the blood is prevented from going back into the right ventricle and then the pulmonary valve opens so that the blood travels through the pulmonary artery towards the lungs.

2. The right ventricle

The right ventricle receives de-oxygenated blood from the right atrium. When it is filled it contracts and the pulmonary valve opens which allows the blood which is under low pressure to flow through the pulmonary artery towards the lungs. After this the pulmonary valve closes to prevent the blood to flow in reverse.

3. Left atrium

The left atrium is the upper right chamber of the heart. The left atrium gets oxygenated blood which is now bright red in colour from the lungs through the pulmonary vein. As the contractions are triggered by the sinoatrial node the blood passes through the opened mitral valve and into the left ventricle.

4. Left ventricle

As the left atrium contracts the left ventricle receives the oxygenated blood. Now the aortic valve which leads to the aorta is closed so that the left ventricle can fill up with the oxygenated blood. When the ventricle is full a lot of blood pressure is created and then the ventricle contracts and the blood flows through the aorta and around the body.

So overall what prevent blood from going the reverse way are the following valves:

-Tricuspid valve

-Mitral valve

-Pulmonary valve

-Aortic valve

The tricuspid valve and the mitral valve are connected to the papillary muscles by a set of tendons called “chordate tendineae”. These tendons are what increase and decrease tension to open and close these valves.  (Please refer to Heart Diagram)