Abstract: The effective period of isolated working guinea pig heart perfused with Tris-sodium-pyruvate solution(Tris-SP)was shown to be 70 rain. Perfluorotributylamine at a concentration of 0.5% added to Tris-SP prolonged the effective time to 90 min. 7-Bromoethyoxybenzene-tetrahydropalmatine (EBP) 10 μmol/L,and prazosin 0.1 μmol/L showed no obvious influence on the parameters in the isolated working guinea pig heart. Methoxamine 1 μmol/L and dopamine 1 /μmol/L produced marked changes on LVP, ABF, +dp/dt_max and T-CO. It is suggested that the a₁-adrenoceptor was partially associated with the positive chronotropic action of the heart. Effects of methoxamine and dopamine on the parameters were antagonized by EBP.It shows that the antagonistic effects of EBP on methoxamine and dopamine are concerned with its antagonistic effection on a₁-adrenoceptor and dopamine reccptor This is consistent with previous results in rabbit aortic strips and tat anococcygeus muscles.