Cardiovascular toxicity including ventricular extrasystoles associated with pheniramine overdosage has been documented in the absence of factors recognised to aggravate this toxicity. The presence of pheniramine and the absence of other compounds was established using analytical techniques. It is concluded that patients with pheniramine overdosage should be treated exercising the same precautions as with tricyclic overdosage. Several sudden and unexpected deaths have occurred due to pheniramine overdosage in both adults and children. The cause of death in each case was not known. The purpose of this report is to document clinical features of pheniramine overdosage, in particular previously unsuspected cardiovascular toxicity manifesting as clinically significant ventricular arrhythmias. Pheniramine was positively identified in the overdosed patient, and the presence of other agents excluded.