Cardiac disease complicating pregnancy is present in a relatively small number of women; however, it accounts for a disproportionate share of maternal morbidity and mortality, especially in developing/emerging countries. The prevalence of cardiac disease in pregnancy is increasing and there are multiple underlying etiologies with wide-ranging severity. Normal adaptions during pregnancy often further challenge already compromised anatomic and physiologic compensatory mechanisms of the cardiovascular system, increasing the risk of adverse maternal and fetal outcomes. In this Element, the authors describe how these changes alter nonpregnant physiology with a variety of preexisting and newly diagnosed cardiac conditions. Maternal and fetal risks are reviewed. Diagnosis and management, from before conception through the postpartum period including appropriate contraception, is discussed. The goal of this review is to increase understanding of the importance of cardiac disease in pregnancy and encourage high-quality multidisciplinary care, and thus improve maternal and fetal outcomes.