Background: The purpose of this study was to determine the incidence and origin of T-wave changes after ablation of an accessory atrioventricular connection (AC), which could either be a sign of damage to the coronary circulation or a result of persistent abnormal repolarization secondary to previously abnormal ventricular activation (“cardiac memory”). Methods and Results: Ninety of 107 consecutive patients (33 women and 57 men, mean age 36 ± 5 years) undergoing successful catheter ablation of an AC were studied. Patients with bundle branch block or more than 1 AC were excluded. Sixty-four patients had manifest preexcitation (group 1) and 26 had a concealed AC (group 2). Immediately after loss of preexcitation, 38 (59%) patients with a manifest AC showed T-wave abnormalities. In contrast, none of the patients with a concealed AC had T-wave abnormalities after ablation (P < .05). The T-wave changes (1) did not correlate with the number or duration of energy applications or with markers of tissue injury; (2) correlated with the location of the AC and the degree of preexcitation, respectively; and (3) completely resolved over a period of weeks to months. None of the patients had recurrence of preexcitation or tachycardia during a mean follow-up of 16 ± 7 months. Conclusions: T-wave changes after ablation are most likely caused by “cardiac memory” and are not a sign of myocardial or coronary injury. (Am Heart J 1999;138:987-93.)