Direct cardiac actions of the H2 receptor agonists, impromidine and dimaprit.

Intracoronary administration of the H2 receptor agonists impromidine and dimaprit at doses that did not alter systemic hemodynamics increased coronary blood flow but had no regional positive inotropic effects. Dose-related increases in myocardial blood flow were observed with both drugs. These effects were attenuated by prior administration of cimetidine. The results of this study demonstrate that H2 coronary receptor stimulation results in vasodilation of both subepicardial and subendocardial regions.