In 1989, adenosine was introduced into the American clinical setting as an antiarrhythmic drug for the acute management of reentrant supraventricular tachycardia involving the atrioventricular node. During this decade of use, evidence for proarrhythmic effects of the drug have been documented. In addition to the mostly benign transient episodes of atrial fibrillation, several cases of life-threatening ventricular arrhythmias induced by adenosine have been reported. This article summarizes the proarrhythmic effects of adenosine as they were reported in the literature as well as data from the manufacturer files. The causes of these adverse effects of adenosine are analyzed, and factors to be considered before using the drug are discussed.