Diphtheria intoxication was simulated in rabbits, by intravenously injecting native diphtheria toxin in a dose of 0.3 MLD (minimal lethal dose) per kg body weight. Intact rabbits were used as a control. Following 1, 3, and 5 days of the onset on intoxication, the chests were opened under 2% rometar anesthesia and the hearts were extirpated, semithin left and right ventricular myocardial sections were prepared and light microscopic morphometry (at a magnification of x 1000) was carried out with video-assisted imaging. The rate of cardiomyocytic (CMC) apoptosis was determined, by calculating the free lying nuclei - the morphologically changed nuclei that were present in the extracellular space. Both ventricular CMC destruction characteristic of necrotic death was ascertained to significantly increase just on day 1 of the experiment and to further enhance during its course. By day 5, the rate of CMC apoptosis increased in both the left and right ventricles. Furthermore, there was an increasing reduction in myocardial collagen levels.