There is growing evidence that sphingosine 1-phosphate (S1P) plays an important role in regulating the development, morphology, and function of the cardiovascular system. There is little data, however, regarding the relative contribution of endogenous S1P and its cognate receptors (referred to as S1P_1–5) to cardiovascular homeostasis. We used S1P₂ receptor knockout mice (S1P₂^−/−) to evaluate the role of S1P₂ in heart and vascular function. There were no significant differences in blood pressure between wild-type and S1P₂^−/− mice, measured in awake mice. Cardiac function, evaluated in situ by using a Millar catheter, was also not different in S1P₂^−/− mice under baseline or stimulated conditions. In vivo analysis of vascular function by flowmetry revealed decreases in mesenteric and renal resistance in S1P₂^−/− mice, especially during vasoconstriction with phenylephrine. In intact aortic rings, the concentration-force relations for both KCl and phenylephrine were right shifted in S1P₂^−/− mice, whereas the maximal isometric forces were not different. By contrast, in deendothelialized rings the concentration-force relations were not different but the maximal force was significantly greater in S1P₂^−/− aorta. Histologically, there were no apparent differences in vascular morphology. These data suggest that the S1P₂ receptor plays an important role in the function of the vasculature and is an important mediator of normal hemodynamics. This is mediated, at least in part, through an effect on the endothelium, but direct effects on vascular smooth muscle cannot be ruled out and require further investigation.