Diphenhydramine overdose in one of the frequent reported causes of acute poisoning. Patients with diphenhydramine overdose can present with central nervous system manifestations, anticholinergic manifestations and cardiovascular symptoms. The cardiovascular symptoms of diphenhydramine overdose include myocardial depression and refractory hypotension. Massive ingestions have been reported to cause myocardial depressant effect with widening of QRS complex and prolonged QT interval on electrocardiogram. We report an adolescent male with moderate diphenhydramine ingestion, who was found unresponsive with seizure like activity. Electrocardiogram on presentation showed wide complex tachycardia with right bundle branch block pattern and QT interval prolongation. These changes reverted to normal with treatment. Diphenhydramine overdose may occasionally result in prolongation of QT interval.