Adenosine is the most recent drug approved for the treatment of paroxysmal supraventricular tachycardia. Its advantage is that it is just as effective as verapamil and is far less toxic. The lack of toxicity is due to the extremely short half-life (one to seven seconds). The mechanism of action of adenosine is different from that of other antiarrhythmic agents. For the specific purpose of ameliorating paroxysmal supraventricular tachycardia, adenosine appears to be an ideal antiarrhythmic drug.