This study was designed to determine if doses of aminophylline up to 10 mg/kg given i.v. would produce ventricular arrhythmias in seven healthy dogs anaesthetized with fentanyl‐dropelidol‐pentobarbital. Arrhythmias were sought by inspection of ECGs before and after attempts at provoking them with 5 pg/ kg boluses of epinephrine given i.v., or by programmed electrical stimulation. After cumulative doses of 10 nig aminophylline/kg body weight, producing an estimated plasma concentration of greater than 30 pginil, no ventricular ectopia other than escape depolarizations were observed. We were unable t o documentan arrhythmogenic effect of aminophylline when given rapidly by the i.v. route. I t is possible that the anaesthetic regimen reduced the arrhythmogenic property of aminophylline, or that arrhythmias might be produced in either obese or ill dogs; but it is unlikely that chronic administration of aminophylline would be more arrhythmoge