Pregnancy is the time when major changes occur in many of the organ functions, blood vessels, and hemodynamics. These changes may include blood volume, heart rate, stroke volume, cardiac output, and systemic vascular resistance. These physiological changes are usually well tolerated by the pregnant woman and must be recognized and understood by the physician in order to distinguish them from what is abnormal. Changes begin early in pregnancy and continue as the pregnancy progresses and are fully reversible after delivery.