Phenylephrine (Neo-Synephrine) hydrochloride was first suggested as an effective drug in the treatment of paroxysmal supraventricular tachycardia by Youmans and his group in 1947. Since this time others have mentioned its use and at the same time suggested that the drug was relatively innocuous in the absence of heart disease. It has been stated that phenylephrine should not be used in the presence of heart disease; however, the specific danger of its use has not been mentioned. We recently treated a patient with paroxysmal supraventricular tachycardia in whom therapy with quinidine, digitalis, apomorphine, ipecac, and procaine amide (Pronestyl) hydrochloride had been ineffective; we therefore chose phenylephrine. The drug stopped the arrhythmia but produced short runs of ventricular tachycardia. For this reason we sought to find if similar experience had been reported and, if so, what significance had been attached to this arrhythmia. We found that the same phenomenon had been