Dimetacrine (0.3 μM) causes no statistically significant decline in contractile force from the controls. Dimetacrine (10 μM), the highest concentration, decreases the contractile force to 36.5±9.1%. Tachycardia is observed after the administration of Dimetacrine (1 to 3 mg/kg, i.v.) and the maximum response is obtained in a dose of 3 mg/kg i.v. Dimetacrine (30 mg/kg. i.v.), induces an abrupt fall in blood pressure with tachycardia or bradycardia followed by cardiac arrest. Respiratory rate increases 40 min after the onset of the infusion of Dimetacrine. However, arterial blood pressure falls 50 min after the onset of the infusion of Dimetacrine.