This report describes & presents results of a study to determine the occurrence of bacterial pathogens in feeder cattle dying from myocarditis and to determine whether an association exists between these death losses and infection with bovine viral diarrhea virus (BVDV). In the study, tissues from heart & lungs of 92 calves dying from myocarditis in Alberta feedlots were immunohistochemically stained for antigens of Hemophilus somnus, Mycoplasma bovis, Mannheimia hemolytica, and BVDV. Tissues from 44 calves dying from non-infectious causes and 35 calves dying from pneumonia were tested as controls. The results indicate the principal pathogen involved in myocarditis and also find differences in the presence of BVDV between calves dying of myocarditis and calves dying of non-infectious causes.