Cardiac and pancreatic lesions were observed in guinea pigs infected with 2 variants (B and D) of encephalomyocarditis (EMC) virus. Cardiac changes were characterized by focal myocardial necrosis and subsequent replacement by immature granulation tissue, and the pancreatic ones by vacuolar degeneration of acinar cells. In the electron microscopic examinations, the affected cardiomyocytes showed intracellular oedema, swelling and/or partial destruction of mitochondria, and distortion and disruption of myofibrils. Intracellular vacuolization and dilatation of rough-surfaced endoplasmic reticulum (rER) were conspicuous in the damaged pancreatic acinar cells. In addition, intracisternal granules were found in dilated rER with a high frequency. These changes were common to animals infected with the B and D variants. On the contrary, B cell alterations; i.e. degranulation and degeneration of insulin granules, were detected only in animals infected with the D variant.