The cardiovascular system consists of the heart and the blood vessels connected to it, and the blood vessels include the arterial and venous systems. The veins connected to the heart are the superior and inferior vena cava and the pulmonary veins, and the arteries connected to the heart are the aorta and the pulmonary arteries. The heart is a hollow, muscular organ with a complex internal structure consisting of four chambers and four sets of valves. The heart is divided into left and right parts by the longitudinal interventricular septum and ventricular septum, which are not interconnected. The left part of the heart flows with oxygen-rich arterial blood, while the right part flows with oxygen-depleted venous blood. The left heart wall is slightly thicker and the right heart wall is slightly thinner. The chambers of the heart include the right atrium, right ventricle, left atrium and left ventricle, which have the function of blood storage and ejection. The heart’s four groups of valves are the tricuspid, pulmonary, mitral and aortic valves, which function as one-way valves to ensure one-way blood flow and no regurgitation. The left and right atria and ventricles have their own atrioventricular valves, which ensure unidirectional blood flow from the atria to the ventricles. The valve between the right atrium and the right ventricle has three leaflets called the tricuspid valve; the valve between the left atrium and the left ventricle has two leaflets called the mitral valve; there is a pulmonary valve between the right ventricle and the pulmonary artery, also with three leaflets; there is an aortic valve between the left ventricle and the aorta, also with three leaflets, and these valves play a vital role in maintaining the unidirectional flow of blood.