Surviving puppies from three separate litters in which deaths had occurred from suspected viral myocarditis were examined clinically and electrocardiographically. Of 11 puppies examined, 5 subsequently died or were euthanised within 11 days of initial examination. ECG changes present in these puppies for 1 to 11 days prior to death were small R waves (less than 0.4 mV in lead II), S-T segment elevation, QRS notching and paroxysmal ventricular tachycardia (PVT). No clinical signs referable to the ECG changes were present before the terminal episodes of apparent sudden death or death following a brief period of dyspnoea. Multifocial subacute myocarditis was present on post-mortem examination. A sixth puppy with small R waves remained clinically normal for a further 4 weeks. It then developed severe dyspnoea which persisted for 24 hours before euthanasia. Extensive fibrosis of the left ventricle was present on post-mortem examination.