The purpose of this study was to evaluate the serial changes in T wave configuration in patients undergoing successful radiofrequency catheter ablation of accessory atrioventricular (AV) connections. Twenty-nine consecutive patients with overt preexcitation and 16 patients with a concealed accessory atrioventricular (AV) connection were included. An electrocardiogram (ECG) was recorded before ablation and 15 min, 1 or 2 days and 1 and 3 months after ablation. Postablation T wave abnormalities occurred in 22 (76%) of the 29 patients who had overt pre-excitation but in none of the 16 patients with a concealed accessory AV connection. The T wave abnormalities were not related to myocardial necrosis or echocardiographic abnormalities. The ECG location and severity of T wave changes were dependent on the accessory AV connection location and degree of baseline pre-excitation, respectively. Fourteen of 19 patients with a posteriorly located AV connection (left, right or septal) had T wave inversion or flattening in the inferior leads and 3 patients had precordial T wave peaking. Two patients with an anteroseptal AV accessory connection had both inferior T wave inversion or flattening and precordial T wave peaking. Among seven patients with a manifest left lateral accessory AV connection, two had lateral T wave inversion or flattening and two had precordial T wave peaking. There was 95% concordance between the directional change of the T wave after ablation and the direction of the delta wave on the baseline ECG.(ABSTRACT TRUNCATED AT 250 WORDS)