Aconitum Koreanum rhizoma has been applied in therapy from old in oriental medicine (Korean Hanbang), The action of the water and alcohol extracts of the rhizoma and root of Aconitum Koreanum R. Raymond, a common herb in Korea, on the isolated Frog heart and LD<sub>50</sub> were observed. The results of the studies were as follows: 1. The cardiac effect in the concentration of the extracts(10<sup>-3</sup>) was increased and duratrin of action prolonged approximately 10 minutes, but in the extracts(3 X 10<sup>-3</sup>)blocked. 2. The LD<sub>50</sub> of extracts were 722 mg/kg (water) and 151mg/kg (alcohol) intraperitoneally in mice.