Pregnancy is a dynamic process associated with significant physiological changes in the cardiovascular system. These changes are mechanisms that the body has adapted to meet the increased metabolic demands of the mother and fetus and to ensure adequate uteroplacental circulation for fetal growth and development. Insufficient hemodynamic changes can result in maternal and fetal morbidity, as seen in preeclampsia and intrauterine growth retardation. In addition, maternal inability to adapt to these physiological changes can expose underlying, previously silent, cardiac pathology, which is why some call pregnancy nature’s stress test. Indeed, cardiovascular disease in pregnancy is the leading cause of maternal mortality in North America.1 This is a review of the normal cardiovascular physiology of pregnancy to provide clinicians with a basis for understanding how the presence of cardiovascular disease may compromise the mother and fetus and how their decisions about medical care may need adjustment.