Experimenting on rabbits, I exposed their pectoral muscles in order to send a direct current of 14-20 volt through their hearts. Corresponding to the heart region I applied a platinum electrode to the muscles until the animals died. Some of them died as early as in 25 minutes under asphyxiating symptoms, while others in 1 1/2 hours. Each heart was taken out at once and put in a 10 per cent. solution of formalin in order to make microscopical sections which were stained with haematoxylin and eosin. In the case where the anode was applied to the heart region the heart muscle fibres became condensed and were stained deeply, showing a shrinkage of their nuclei which take up especially much stain. Macroscopically the surface of the heart showed an excavation. In the case where the cathode was put on the heart region, the cardic muscle fibres became loose, staining only lightly. Above all the nuclei were stained slightly and showed a swollen aspect. Macroscopically the surface of the heart corresponding to the place of the electrode was convexed. Concerning the cause of the above mentioned facts, I am of opinion that the electroendosmose plays the most important role. On account of the water stream which is directed towards the cathode the tissue becomes loose and edematous in the cathodic region and condensed in the anodic. Besides the quotient of K/Ca which becomes geater in the cathodic place and smaller in the anodic must be taken into consideration.