100 turkey poults (1 day of age) were housed in 16 boxes, each containing 6-7 animals. In each case 4 boxes constituted 4 feeding groups. One was the control group and the other three received a feed containing different quantities of the mycotoxin moniliformin (0.8; 1.6; 2.4 mg/kg) and beauvericin (0.8; 1.7; 2.5 mg/kg). The animals were fed for 12 weeks and then slaughtered. Pieces of the heart were examined by routine histology. The microscopical evaluation showed cell infiltration into the heart muscle and alterations of the heart muscle. However, a relation could be detected between the mycotoxin concentration in the feed and the frequency and the quality of heart alterations.