Unmasking of a second atrioventricular accessory connection by adenosine in a child with a long RP' reentrant tachycardia.

A second unidirectional, retrograde accessory atrioventricular pathway was unmasked by adenosine during the intracardiac evaluation of a child with a reentrant long RP' tachycardia. This case is further evidence of the value of adenosine during the evaluation of these types of tachycardias.