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The heart is the muscle organ of human and other animals. It draws blood through the blood vessels of the circulatory system. Blood provides oxygen and nutrition for the human body and helps to remove metabolic waste. In humans, the heart is between the lungs, in the middle of the chest.

In humans, other mammals and birds, the heart is divided into four chambers: the upper left and right atrium; the upper left and right atrium. And the lower left and right ventricles. Usually, the right atrium and ventricle are called the right heart, and the left ventricle and the left ventricle are called the left heart. In contrast, fish have two chambers, one atrium and one ventricle, while reptiles have three. In a healthy heart, because of the heart valve, blood flows through the heart in a way that prevents backflow. The heart is encased in a pericardial protective capsule, which also contains a small amount of fluid. The heart wall consists of three layers: epicardium, myocardial layer and endocardium.

The heart draws blood at a rhythm determined by a group of pacemaker cells in the sinoatrial node. These currents cause the heart to contract and move through the atrioventricular node and along the heart's conduction system.

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