Gastric dilatation was diagnosed in 156 dogs during a 5-year period. The recurrence rate was 10% and the overall mortality was 43%. Large-breed dogs of either sex and ranging in age from 2 months to 15 years (mean age, 5.2 +/- 2.9 years) were found to be susceptible to the problem. Cardiac arrhythmias were diagnosed in 48 of 115 (42%) affected dogs. Cardiac arrhythmias occurred most frequently between 12 and 36 hours after the onset of gastric dilatation-volvulus and were generally ventricular in origin.