Heart

===The Heart is a hollow muscular organ that pumps blood through the circulatory system. The superior vena cava and the inferior vena cava are either of two large veins discharging blood into the right atrium of the heart, one superior vena cava conveying blood from the head, chest, and upper extremeties. Aorta is the main trunk of the arterial system, it conveys blood from the left ventricle of the heart to all of the body except the lungs. The Right and Left Atrium are two upper chambers on each side of the heart that receives blood from the veins and force it into the ventricles. The Right and Left Ventricles are two lower chambers on each side of the heart that receive blood from the aorta and force it into the arteries. Pulmonary valves are semilunar valves between the pulmonary artery and the right ventricle of the heart that prevents blood from flowing back into the right ventricle. The Aortic valve is a semilunar valve between the aorta and the left ventricle of the heart that prevents the blood from flowing back into the ventricle. Mitral valve is a valve between the left atrium and the left ventricle of the heart. It consist of two triangular flaps of tissue that prevent the blood from flowing back into the atrium. Pulmonary vein is a vein conveying oxygenated blood from the lungs to the left atrium of the heart. Pulmonary artery is the artery conveying venous blood from the right ventricle of the heart to the lungs.===