The normal human heart is a hollow, muscular organ that functions as a “blood pump” to maintain blood circulation throughout the body. The atrial septum, ventricular septum and left and right atrioventricular orifices separate the heart into four chambers: the right atrium, right ventricle, left atrium and left ventricle, which are connected to the upper and lower vena cava, pulmonary arteries, left and right pulmonary veins and the aorta, respectively. On the surface of the heart there is also the heart’s own circulatory system, namely the coronary arteries and coronary veins. Between the right atrioventricle and the left atrioventricle are a set of atrioventricular valves called the tricuspid and mitral valves, respectively. They are unidirectional valves that allow blood to flow from the atria to the ventricles and prevent it from flowing in the opposite direction (i.e., ventricle to atrium). There are also a set of semilunar valves between the right ventricle and the pulmonary artery and between the left ventricle and the aorta, called the pulmonary valve and the aortic valve, respectively. Again, they are unidirectional valves that allow blood to flow from the ventricle to the artery and prevent blood from flowing from the artery to the ventricle. It is the presence of these atrioventricular and semilunar valves that ensures that the heart performs its “pumping” function with blood flowing in a certain direction, over and over again, without regurgitation. The direction of blood flow is: Upper and lower vena cava → right atrium → right ventricle → pulmonary artery → pulmonary circulation → pulmonary veins → left atrium → left ventricle → aorta → body circulation → upper and lower vena cava