The term tachycardiomyopathy refers to a specific form of tachycardia-related cardiomyopathy caused by supraventricular or ventricular tachyarrhytmias that are associated with ventricular rates higher than 120 bpm. The arrhythmias most frequently associated with these forms of heart disease are the atrial fibrillation and atrial flutter, particularly in the elderly population and the most frequent clinical manifestation is the heart failure. Here we report the clinical case of a patient that came to our attention because of an episode of heart failure associated with prolonged and repetitive strips of rapid conduction with wide QRS morphology doubtful for pre excitation or ectopia in the context of atrial fibrillation and atrial flutter. We showed that those strips of tachycardia with wide QRS, when associated with atrial flutter in particular, were so fast and consistent to determine the left ventricular contractile dysfunction; also we showed that those strips of wide complex tachycardia were caused by pre-excitation through an accessory right posteroseptal pathway and supported by the reentry circuit of the common atrial flutter. The block of conduction through the accessory pathway and the elimination of atrial arrhythmia allowed the regression of left ventricular contractile dysfunction. We believe that this case is interesting because it shows that there is a strict continuity between sophisticated electrophysiological mechanisms and clinical manifestation