A syndrome on four dairy farms in which calves up to two months of age died suddenly during a period of excitement usually precipitated by feeding was investigated. The description given by owners was that during, or shortly after milk feeding, the calves grunted, fell and died within one minute. Post mortem examinations revealed patchy myocardial pallor but no other lesions or evidence of infectious disease. Histopathological studies revealed peracute myocardial degeneration. Biochemical examinations have shown a selenium deficiency in in-contact calves and since this was corrected, no further cases have occurred. It is suggested that this is an additional manifestation of the selenium deficiency syndrome and that in certain circumstances, a deficiency of available selenium renders cardiac muscle vulnerable to stresses which induce severe peracute damage and leads to cardiac failure and sudden death.