The heart is located slightly to the left of the middle of the thoracic cavity, between the two lungs and above the diaphragm, with the sternum and rib cartilage in front and the esophagus and spine behind. The normal heart is the size of my fist. The large blood vessels of the human body, the aorta, pulmonary artery, superior vena cava, and inferior vena cava, enter and exit the heart. The heart is a muscular organ of the human body and consists of special cardiac smooth muscle – cardiomyocytes. The heart works non-stop throughout a person’s life and functions as a power blood pump, responsible for the circulatory flow of blood throughout the body. The interior of the heart is divided into four chambers by the upper and lower interatrial septum and septum and the left and right atrioventricular valves: the right atrium, the right ventricle, the left atrium and the left ventricle. The left ventricle and right atrium are thin-walled chambers that serve to pump blood. The right atrium has a population of superior and inferior veins that receive blood returning from the whole body; the right atrium is connected to the right ventricle through the tricuspid valve, and blood enters the right ventricle from the right atrium. The outlet of the right ventricle has a pulmonary valve, which opens when the ventricle contracts and blood flows into the pulmonary artery through the pulmonary valve, and closes when the ventricle is diastolic to prevent blood from flowing backward into the right ventricle. There are two pulmonary vein openings on each side of the left ventricle. The left atrium is connected to the left ventricle through the mitral valve, and blood flows from the left atrium into the left ventricle, which has an opening for the aortic valve. Blood flows through the aorta during ventricular contraction and closes through the aortic valve during ventricular diastole to prevent blood from flowing backwards into the do ventricle. Congenital heart disease occurs when the basic anatomy of the heart is not fully developed at birth or when there are developmental abnormalities. When any one or more of the four valves of the heart become narrowed or incompletely closed, the normal flow of blood is affected and a heart valve lesion develops.