Action of acetylcholine on the atropinised heart of the frog during summer months.

: During summer months high doses of acetylcholine produced positive inotropic and chronotropic actions in 19 out of 22 preparations of atropinised perfused heart of the frog. Hexamethonium failed to block both the positive inotropic and chronotropic actions of Ach. Interestingly another ganglion blocking agent mecamylamine as well as beta adrenergic blocking agent propranolol blocked the positive inotropic action but not the positive chronotropic action.