The effects of impromidine (16 nmol/kg intravenously) were studied in the general and coronary circulations of the intact anaesthetized dog. 2. The drug caused tachycardia, increased cardiac output and coronary sinus flow, and induced minor changes in systemic and pulmonary arterial pressures. 3. It increased left and right ventricular work, and decreased calculated resistance values in the greater and lesser circulations. Coronary vascular resistance fell, cardiac O2 extraction increases. 4. These changes were substantially prevented by treatment with cimetidine. 5. The action of an H2-receptor agonist then is associated with a general and coronary vasodilator response, with maintenance of calculated cardiac efficiency.
