The central topic is the modification of the respective action potentials or ion flows of isolated myocards under various experimental conditions. The following issues are considered: the patch-clamp and voltage-clamp techniques (animation); origination of the action potential (animation); the effects of cadmium and adrenaline (action potentials, ion flows, optical cinemicrography); the interpendency between action potential and stimulation frequency or the absolute and relative refractory period, respectively (with simultaneous display of cinemicrographs and action potentials).