Phentolamine-d 4 (hydrochloride) is the deuterium labeled Phentolamine hydrochloride. Phentolamine hydrochloride is a reversible, non-selective, and orally active blocker of α1 and α2 adrenergic receptor that expands blood vessels to reduce peripheral vascular resistance. Phentolamine hydrochloride can be used for the research of pheochromocytoma-related hypertension, heart failure and erectile dysfunction.