Heart rates of healthy cows and cows suspected of having bovine spongiform encephalopathy were measured by auscultation and by a portable cardiac monitor. Bradycardia was demonstrated in suspect cases which were confirmed histopathologically. Disturbances in cardiac rhythm were also evident in some cases. Healthy cows deprived of food exhibited bradycardia. The administration of pharmacological doses of atropine indicated that bradycardia in BSE was mediated by increased vagal influence, suggesting that the cardioinhibitory reflexes in the caudal brainstem were functionally altered by the disease.