Korean aconitum (Aconitum koreanum R. Raymond) as one of the botanical crude drugs which pertain to helleboraceae has been extensively applied in Chinese medicine during the past decades. It has been particularly used in immortal tonic among the folk remedies in China, however, its general uses comprehend diuresis, cardiotonic, analgesia, neuralgia, gout and, furthermore, even neoplastic effect. The components of aconitum have been acknowledged as aconitine, mesaconitine, hypaconitine, aconine and so on. The main ingredient, aconitine has the advantage of causing the atrial fibrillation, but, its pharmacological research has not been fully elucidated. Although there are many reports with regard to the pharmacological effects on the motility of several animal hearts, their conclusions have not been regretfully coincided yet. The authors hereby paid attention to this point of view and made experiment to examine the relationship between the alcohol extract of Korean aconitum and the motility of the isolated clam heart, making the use of several drugs related to the heart such as serotonin, acetylcholine, pilocarpine, physostigmine, barium chloride, procaine and quinidine. The cardiac movement of the isolated clam (Meretrix lusoria) heart in the standard sea water solution was recorded with the electric kymograph according to the Magnus method. The results of the experiment are as follows. 1. The motility of the isolated clam heart represents the tendency of gradual inhibition in proportion to the concentration of AK-A 10^-4, 5 X 10^-4, and 10^-3. 2. The cardiac inhibitory effect of AK-A 10^-3 antagonizes the motility of the isolated clam heart pretreated with serotonin 10^-6. 3. The cardiac inhibitory effect of AK-A 10^-3 antagonizes the systolic state appealed by barium chloride 10^-3. 4. The systolic state caused by quinidine 10^-4 is not inhibited by AK-A 10^-3.