Structure of Human Heart\tThe heart is a muscular organ covered by a double membrane called pericardium.\tThe pericardial fluid of the pericardium lubricates the heart.\tThe heart is divided into four chambers — two upper atria and two lower ventricles.\tThe inter-atrial septum separates the two atria and the inter-ventricular septum separates the two ventricles.\tThe atrium and the ventricle of each side are separated by the atrioventricular septum.\tSuperior and inferior vena cavae open into the right atrium.\tThe right ventricle opens into the pulmonary artery.\tFour pulmonary veins open into the left atrium.\tThe left ventricle opens into the aorta.\tThe opening between the right atrium and right ventricle is guarded by the tricuspid valve.\tThe opening between the left atrium and left ventricle is guarded by the bicuspid (mitral) valve.\tThe opening of the right ventricle into the pulmonary artery and the opening of the left ventricle into the aorta is guarded by the semilunar valves.Working of Heart\tThe right atrium receives blood from the upper and lower body through the superior vena cava and the inferior vena cava, respectively, and from the heart muscle itself through the coronary sinus. The right atrium is the larger of the two atria, having very thin walls. The right atrium opens into the right ventricle through the right atrioventricular valve(tricuspid), which only allows the blood to flow from the atria into the ventricle, but not in the reverse direction.\tThe right ventricle pumps the blood to the lungs to be reoxygenated.\tThe left atrium receives blood from the lungs via the four pulmonary veins. It is smaller than the right atrium but has thicker walls. The valve between the left atrium and the left ventricle, the left atrioventricular valve(bicuspid), is smaller than the tricuspid. It opens into the left ventricle and again is a one-way valve.\tThe left ventricle pumps the blood throughout the body through the aorta, which\xa0is the\xa0largest artery in the body. The walls of the left ventricle are the thickest among all the chambers.

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