Prostacyclin (PGI2, epoprostenol), a pulmonary and systemic vasodilating agent, has recently undergone long-term intravenous administration trials in patients with severe congestive heart failure. As in many other agents that have beneficial acute hemodynamic profiles, its effects on mortality have been disappointing. However, the drug continues to have a role in the short-term management of patients with decompensated heart failure because of its short half-life, lack of medium-term toxicity compared to sodium nitroprusside, and lesser tendency toward development of tolerance than intravenous nitrates. There may also be therapeutic effects other than its influence on central hemodynamics; in particular, inhibition of platelet aggregation and thrombus formation in small vessels may be of value in the long-term management of patients with primary pulmonary hypertension. It is possible that, like other agents such as vesnarinone (OPC-8212), achieving beneficial long-term effects may require identification of an ideal dose range. The most effective therapeutic doses in long-term administration may not correlate with the most effective doses during short-term hemodynamic studies.