This article focuses on a newly discovered bioactive peptide, termed apelin, as it relates to the cardiovascular system. Apelin, through its G-protein coupled receptor, seems to primarily exert effects in blood pressure control, and may play a role in heart failure and in myocardial reperfusion injury. In addition, at least some of apelin's effects appear to stem from an interaction with the renin-angiotensin system. Apelin may provide a target for drug treatment of cardiovascular disease.