Bioassay-guided fractionation of an n-BuOH extract of the lateral roots of Aconitum carmichaeli. led to the isolation of 5 cardioactive C(19)-diterpenoid alkaloids: N-deethylaconine (1), beiwutinine (2), hypaconine (3), mesaconine (4), and 15α-hydroxyneoline (5). N-Deethylaconine and beiwutinine are new aconitine-type C(19)-diterpenoid alkaloids. Hypaconine was isolated from this species for the first time. Among them, mesaconine, hypaconine, and beiwutinine showed the strongest cardiac actions on the isolated perfused bullfrog heart. Furthermore, mesaconine has protective effects, including improved inotropic effect and left ventricular diastolic function, on myocardial ischemia-reperfusion injury in rat at a dose of 10(-9) mol/L. However, mesaconine has almost no effect on heart rate.