Actions of acetylcholine, atropine, epinephrine and quinidine on heart muscle of cat

Mammalian heart muscle has basic characteristics of resting excitability, re-fractory period, contractility and spontaneous rhythmicity. With the advent of the use of electronic stimulators of new design and the use of the oscilloscope to measure the amplitude and duration of minute currents more accurate study has become possible. In a previous communication the normal range of variation of these fundamental properties of heart muscle have been defined (DiPalma and Mascatello, 1951). In this investigation the effect of acetylcholine, atropine, epinephrine and quinidine has been studied on the isolated auricle and papillary muscle of the cat. It is hoped that the results will put on a more definite basis the fundamental properties of these commonly used drugs about which opinion seems divided (Lewis and Drury, 1926; Wedd and Blair, 1942; De Elio, 1947). Methods. The technique of measuring the refractory period and the resting excitability of the isolated heart muscle have been previously described (DiPalma and Mascatello, 1951). Briefly it consisted of suspension of the muscle in Locke’s solution in a manner de-scribed by White and Salter (1946), so that short circuiting of the electrodes did not occur