Prostacyclin is a potent vasodilatory and antiplatelet eicosanoid produced by endothelial cells that inhibits platelet aggregation and promotes blood vessel relaxation. It plays a critical role in maintaining vascular homeostasis and preventing thrombosis, especially in the pulmonary circulation. Deficiency or dysfunction of prostacyclin is implicated in conditions such as pulmonary arterial hypertension, where impaired vasodilation and increased clotting contribute to disease progression.