Intracardiac infusion of acetylcholine in primary pulmonary hypertension

Two cases of primary pulmonary hypertension are presented, and the results of right heart catheterization are given. Infusion of acetylcholine caused large decreases in pulmonary arterial pressure in one subject, both at rest and during exercise. In the second subject, infusion of acetylcholine resulted in a lesser but still significant decrease in pulmonary arterial pressure. The criteria that must be met before conclusions are drawn as to the existence of vasodilation or vasoconstriction in the pulmonary vascular bed are discussed.