Twenty five patients aged 6 to 35 years (mean +/- SD: 14.2 +/- 7.1 years), surgically corrected for tetralogy of Fallot (TOF) more than one year ago, were assessed for rhythm abnormalities by resting electrocardiogram (ECG), twenty-four hours ambulatory ECG monitoring, signal averaged ECG and electrophysiological studies. An X-ray chest for assessing heart size, two dimensional and Doppler echocardiography for residual defects and radionuclide angiography for resting left ventricular ejection fraction were also done. Eight out of 25 (32%) patients were found to have significant rhythm abnormalities. Ventricular arrhythmias were detected in four patients. In two, ventricular tachycardia was induced during electrophysiologic studies, being sustained in one. Multiform ventricular ectopics were observed in two other patients. All these patients were operated, after the age of 10 years, and three of them are presently more than 20 years old. Cardiomegaly was present in the chest X-ray in three patients, and significant residual pulmonary stenosis was seen in one patient. Left ventricular ejection fraction was reduced in two, while signal averaged ECG was positive in one of the three cases subjected to this investigation. Supraventricular tachycardia (SVT) was observed in three patients. This was diagnosed by ambulatory ECG monitoring in all but in addition, was also inducible in one patient on electrophysiologic testing. There was no correlation of the occurrence of SVT with age or age at correction for TOF. None of these patients had any residual defect, cardiomegaly or subnormal left ventricular ejection fraction. Transient complete heart block requiring temporary pacing was documented in one patient with a large residual ventricular septal defect.(ABSTRACT TRUNCATED AT 250 WORDS)