Tachyarrhythmia in a St Bernard dog.

A young St Bernard dog was referred on three separate occasions for investigation of dyspnea and exercise intolerance. Electrocardiography was performed on each occasion and showed various forms of supraventricular tachycardia with aberrant conduction. Echocardiography showed a progressive decrease in systolic function and thoracic radiographs showed progressive cardiomegaly. The arrhythmia responded rapidly to treatment with propanolol.