Origin and extinction of current due to damage caused by suction electrode on frog heart was studied. By means of epicardial and intracellular leads it was found out that this demarcation current manifests itself only in a very limited space around the place of suction and does not differ from the current due to damage caused by restraint in the coronary bloodstream in hearts of warm-blooded or in myocardial infarction in man. Membrane depolarization degree is diminishing from the place of suction with all accompanying manifestations also in intracellular recordings. The main cause of these changes is the local raised concentration of extracellular potassium ions and the participation of sodium and calcium ions is also being considered. It was proved that this simple biological model of current due to damage is suitable for the study of some changes in electrical heart area and in this way depolarizing and repolarizing parts of the electrocardiogram also in the ischemic heart disease in man.