The possibility of multiple accessory atrioventricular pathways as that of multiple atrioventricular "nodal" pathways represents a relatively usual finding in patients suffering from supraventricular reciprocating tachycardias; the occurrence of both double atrioventricular nodal and concealed accessory pathways in the same patient, on the contrary, is far less common, and is usually an unsuspected condition prior to an electrophysiologic endocavitary study. The authors describe a patient suffering from paroxysmal tachycardias of both types, which have been clearly demonstrated by a transesophageal electrophysiological study. The report shows the different effects of two drugs, verapamil and flecainide, on these reciprocating circuits. Flecainide showed an immediate effectiveness in this condition, while verapamil, although very effective for the "nodal" reciprocating tachycardia, might worsen the accessory reentrant one, and cause a "jump" from the first to the second form.