Of 175 patients treated surgically for potentially lethal or refractory cardiac tachyarrhythmias, 53 underwent mapping and definitive operation using cryoablative techniques as the primary or adjunctive method. Included were 16 patients with supraventricular tachycardia caused by accessory pathways (Kent bundle) in the right anterior or posterior paraseptal location. Cryoablation was successful in abolishing tachycardia in 93.7% (15 of 16). Six patients (100%) with permanent junctional reciprocating tachycardia were cured by cryoablation. Eighteen of 19 patients with atrial ectopic tachycardia were treated by cryoablation alone or in combination with excision of the atrial appendage, with success in 15 (83.3%). Five of these were left atrial foci cured by cryoablation. Fourteen right atrial foci were treated by excision of the appendage only (1 patient), excision of the appendage and local cryoablation (8 patients), and cryoablation alone (5 patients). Three of these underwent partial (2 patients) or complete (1 patient) atrial disconnection after excisional and cryoablative techniques failed to control the tachycardia. Multiple ectopic atrial foci were common (9 patients), and successful cryoablation was accomplished in 100% of the patients with a single atrial ectopic focus (10 patients) but in only 66% of those with multiple foci. Thirteen of 19 infants with critical ventricular tachycardia were treated by cryoablation at the site of the ectopic focus, either alone or in combination with excision of the area. Elimination of tachycardia was accomplished in 13 patients (100%). Myocardial hamartoma (Purkinje cell tumor) was the histological diagnosis in 11 of the infants with ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)