Over the past four decades, maternal adaptation to pregnancy has been the subject of extensive medical research, which has revealed the massive change that the mother’s cardiovascular system undergoes to support the growing fetus. This chapter describes the increase in heart rate, stroke volume, and cardiac output and the fall in systemic vascular resistance, mean arterial pressure, and vascular compliance that occur during gestation, delivery, and the post-partum period. We shall also discuss the hormonal mechanisms that underlie these changes and how they relate to intrinsic maternal characteristics, such as maternal age, parity, ethnicity and body mass index, and external environmental factors, including living at altitude and diet.