Minipig breeds are being used as experimental animals in medico-biological research. The cardiovascular system of the pig frequently serves as the model for the human cardiovascular system. Histopathological myocardial alterations which may have an impact on the survivability in stress situations can be proven in clinically healthy fattened pigs. The objective is to examine whether similar myocardial alterations are present in minipigs. These processes must be distinguished from phenomena which result in the course of the use of the animals for research purposes. The present thesis is thus aiming at the completion of the spectrum of criteria concerning the experimental animal Berlin minipig. The hearts of 87 Berlin minipigs were examined. They were classified into different age groups (1, 2, 3, 6, 12, 24 months). 9 and/or 8 myocardium samples taken from each heart were prepared with hematoxylin and eosin staining, and 1 with Sudan red G staining. The following criteria were considered in the histological examination: inflammations, degenerations and necroses, fatty degenerations, dystrophic calcinoses, sarcosporidiosis as well as vascular alterations. The findings were collected semiquantatively by classifying them into different degrees of severity, they were compared with each other and statistically evaluated. For 35 hearts, the Luxol Fast Blue staining was applied in addition. The method of stunning was taken into account when the evaluation was made. The histological examination showed that pathological myocardial findings can be detected in clinically healthy Berlin minipigs. These alterations are age- dependent. Inflammatory processes had the highest incidence. The portion of tissue samples showing the said pathohistological alterations was 3.4 % of the tissue samples examined in the first month of life, it rose to a maximum of 38.9% at an age of 12 months and it fell to 24.4% in the 24th month of life. The portion of tissue samples showing degenerative and necrotic alterations was 25.6% at an age of 12 months, and 14.4% at an age of 24 months of life. No degenerative necrotic alterations were found in the 1 month old animals. Degeneration and necrosis were always connected with inflammatory alterations. Dystrophic calcinosis was only found in one tissue sample of the 6-month-old Berlin minipigs. No degenerative fatty infiltration was found in any of the preparations. The portion of tissue samples with Sarcosporidia cysts varied between 0% (1 and 2 months) and 30% (12 months). Muscular-elastic intima proliferations at the intramural coronary arteries were found with a higher incidence with increasing age. The degree of severity of these processes was age-dependent, too. The first presence of swellings of the intima and of the media was proven in 6-month-old animals (10.5% of the hearts). At an age of 12 and 24 months, their share was 50% each. Intima-media swellings were exclusively found in the papillary muscles. The LFB staining is used for the detection of the myofibrillar degeneration as a form of early myocardial damage. The myofibrillar degeneration may occur in a diffuse form or as a myofibrillar degeneration of the transverse band type. An LFB-positive myocardial damage could be proven in 82.9% of the hearts that were examined. The animals stunned by the captive bolt pistol showed 75% of LFB-positive myocardial damage, and the animals stunned by electroshock had a positive reaction to LFB of 93.3%. Two thirds (66.7%) of the pigs stunned by means of electroshock showed a moderate reaction. 13.3% of the hearts showed a moderate to severe myocardial damage. 6.7% each of the hearts of the pigs that had been stunned by means of electroshock showed a mild and a mild to moderate damage. In 6.7% of the hearts of this group no LFB-positive reaction could be determined. 25% of the animals stunned by the captive bolt pistol showed a moderate damage. 15% of them had the transitional form of a mild to moderate damage. In 25% of the hearts of this examination group no LFB-positive damages at all could be proven. In one preparation each of the two groups that were examined, the myofibrillar degeneration of the transverse band type was proven whereas the remaining LFB-positive myocardial samples showed the diffuse type. An artifical damage of the cardiac muscle by the stunning and killing process itself seems to be given. Consequently, the significance of LFB staining for the determination of early myocardial damage in killed miniature pigs not caused by stunning is to be termed unreliable. The results show that pathohistological myocardial alterations can be proven in clinically healthy Berlin minipigs. The incidence and the degree of severity of the pathomorphological alterations are at the same level as was also determined for slaughter pigs of a different genetic stock. Infectious, infectious-toxic and metabolism-induced factors as well as repeated stress- induced micronecroses must be taken into consideration as the cause of the said alterations. When using the Berlin minipig in biomedical research, the presence of these natural myocardial alterations must be taken into account.