Seven of 17 patients with incessant supraventricular tachycardia caused by an accessory pathway with a long retrograde conduction time were seen with symptoms or echocardiographic signs of a tachycardia-induced cardiomyopathy. Three patients were in New York Heart Association functional class II with dyspnea and four were in class III. Eight patients (six with tachycardia-induced cardiomyopathy) underwent surgery because of failure of medical treatment (including one patient in functional class I) and one underwent direct current catheter ablation of the atrioventricular (AV) node. In six patients echocardiograms recorded before and after the procedure were available. Before surgery or direct current ablation the mean left ventricular ejection fraction was 36.3 +/- 8.7%, the left ventricular end-diastolic diameter 55.7 +/- 7.6 mm and the left ventricular end-systolic diameter 44.3 +/- 7.8 mm. A mean of 21.6 +/- 6.8 months after the procedure the mean left ventricular ejection fraction increased to 58.6 +/- 8.0%, the left ventricular end-diastolic diameter decreased to 49.0 +/- 3.6 mm and the left ventricular end-systolic diameter decreased to 32.2 +/- 2.7 mm; all six patients were in functional class I. These results confirm that control of incessant tachycardia leads to a regression of symptoms and signs of cardiomyopathy and progressive normalization of the dimensions of the heart. Because of these findings, surgery should be considered early in patients with an accessory AV pathway and incessant tachycardia. The presence of a tachycardia-induced cardiomyopathy should therefore be an indication for surgery rather than a contraindication.