Abstract
1. Aconitine-induced arrhythmias of the isolated rabbit atria and ventricles, recorded by the microelectrodes, disappeared in the Na-free choline-substituted Tyrode solution.
2. Tetrodotoxin antagonized the aconitine-induced irregular electrical activity of the atria and ventricles, restituting the regular rhythms.
3. MnCl2 which affects the Ca permeability did not abolish the aconitineinduced irregular activity of the atria and ventricles
4. These data indicate that the principal cause of aconitine-induced irregular firing of the atria and ventricles seems to be due to enhancement of the rapid inward Na current.
