Normal Heart

Provided by "Pediatric Heart Surgery — a reference for professionals"

The normal heart has two primary functions; first, to propel blood to the pulmonary capillaries to become oxygenated, and second, to propel blood that has been oxygenated to the systemic capillary beds. This “two-pump” system works together in series. Blood that has been depleted of some of its oxygen returns to the right side of the heart via the superior and inferior vena cavae. This blood is roughly 75% to 80% saturated. Once blood reaches the right atrium, atrial contraction helps fill the right ventricle just prior to ventricular systole. During ventricular systole, blood is ejected through the pulmonary valve to the lungs via the pulmonary artery. The normally low pulmonary vascular resistance allows for unhindered passage of blood through the pulmonary arterial tree. Gas exchange occurs at the pulmonary capillaries of the alveoli. Next, fully saturated blood returns to the left atrium via the pulmonary veins and atrial systole augments filling of the left ventricle just prior to ventricular systole. During left ventricular systole, blood is ejected through the aortic valve to the aorta to be delivered to the organs of the body and peripheral tissues.

This “two-pump” system is efficient and capable of performing at extremes of activity level. The right ventricle pumps blood to a low pressure, low resistance capillary bed. The left ventricle, however, must pump blood to the entire body. Perfusion of this massive network of vessels and capillaries requires significantly higher pressure. The morphology of the left ventricle differs from that of the right ventricle. The left ventricle is thicker than the right ventricle. This is consistent with the higher pressure normally generated by the left ventricle. In addition, the left ventricle has a football shape that is more efficient for generating high pressure. The right ventricle is thin walled and wraps partially around the left ventricle. Consistent with the thin wall of the right ventricle is its high relative compliance (small changes in pressure create large changes in volume). This allows the right ventricle to accommodate rapidly to changes in cardiac output. The efficient function of the heart depends on normal structural anatomy, normal pulmonary and systemic vascular resistances, and normal atrioventricular synchrony. Congenital heart disease can affect some or all of these.