The Heart muscle

This article is about the heart and how it works in the body. Every heart is made up of three layers. An inner lining called the endocardium, a middle layer of muscle called the myocardium, an outer fluid-filled sac known as the pericardium. The heart is divided into four chambers each of the chambers has valves. The valves have different names. The tricuspid valve is at the exit of the right atrium, mitral valve is for the left atrium pulmonary valve is at the exit of the right ventricle the aortic valve is at the exit of the left ventricle. Their purpose is to allow blood to move forwards through the heart and to prevent it flowing backwards into the previous chamber.
The heart muscle contracts in two stages to squeeze blood out of the heart. The blood is pumped from the right atrium down into the right ventricle and from the left atrium down into the left ventricle. In the second stage, the lower chambers contract to push this blood out of the heart to either the body via your main artery (aorta) or to the lungs to pick up oxygen.

| On the right side, the upper chamber fills with oxygen-depleted blood from your body and pushes it via the lower chamber and the pulmonary artery back to the lungs. Here blood picks up oxygen and releases carbon dioxide. On the left side, the upper chamber fills with oxygen-rich blood from the lungs. This is pumped via the lower chamber into the aorta and out to the body to provide cells with the crucial oxygen