Late noninvasive evaluation of cardiac performance in mildly symptomatic older patients with Ebstein's anomaly of tricuspid valve: role of radionuclide imaging. Ten patients 8 to 54 years of age with isolated Ebstein's anomaly of the tricuspid valve were evaluated by electrocardiography, maximal exercise treadmill testing, 24 h electrocardiographic (ECG) monitoring, echocardiography and rest radionuclide imaging of the left ventricle. The patients presented after the 1st year of life and had not undergone surgical intervention. All except one were in functional class II. No patient had preexcitation on the surface ECG, but abnormal tachyarrhythmias or bradyarrhythmias were seen in five patients on 24 h ECG monitoring. Subnormal exercise performance was observed in five patients. Echocardiography demonstrated typical variable tricuspid valve displacement and paradoxic interventricular septal motion. Left ventricular end-diastolic dimensions were normal in all patients, but posterior wall motion was reduced in two. Moderate to severe tricuspid regurgitation with a Doppler jet velocity less than 2.5 m/s was demonstrated in eight patients. Left ventricular radionuclide scintigraphy revealed a subnormal ejection fraction (less than 50%) in 5 of 10 patients; these 5 had previously shown suboptimal exercise performance. The two youngest patients (less than 15 years) had no arrhythmia, normal exercise performance and normal left ventricular ejection fraction. There was no correlation between the degree of tricuspid valve displacement or regurgitation and the presence of rhythm disturbance, exercise performance or radionuclide left ventricular function. Late evaluation of patients with Ebstein's anomaly may demonstrate significant unsuspected abnormalities in cardiac rhythm, exercise performance and left ventricular function. Radionuclide scintigraphy is a useful noninvasive technique for assessing left ventricular dysfunction in these patients. 