Four patients suffered a distinctive neurologic syndrome after undergoing profound hypothermia and complete circulatory arrest for congenital heart lesion repair. Symptom onset was delayed 24-120 hours postoperatively. The syndrome consists of choreoathetosis and oral-facial dyskinesias, hypotonia, affective changes, and pseudobulbar signs (CHAP). Precise anatomic localization is uncertain. Magnetic resonance imaging of 2 patients did not reveal basal ganglia lesions. Pathogenesis is obscure.