PURPOSE--To analyze the characteristics of atrial (A) and ventricular (V) electrograms, AV and VA intervals relation to determine a precise radiofrequency ablation site. METHODS--A and V electrograms (EG) recorded at successful (group 1) and unsuccessful (group 2) sites in 22 patients submitted to RF catheter ablation were identified. Specific criteria as morphology, AV and VA intervals relation and the presence of an accessory pathway were analyzed. RESULTS--The shortest AV interval with a VEG that precedes the delta wave in the onset of the QRS recorded at the EKG leads was the best outcome predictor. The AV connection potential was only recorded in five out of 22 patients and did not interfere with the result when not present. The interval measured between the onset of the V electrogram and the onset (delta wave) of the QRS complex (V-d) varied from -4.9 to -11msec (m = 7.5 + 1.6) in G1 and from -6 to 15msec (m = 9.6 +/- 3) in G2 (p = 0.03). Unsuccessful sites had the VEG preceding the delta wave but the AV interval was not short. Success in the retrograde mapping of target site seems to be the presence of an atrial potential that occurs simultaneously with the nadir (S wave) of the QRS complex. CONCLUSION--Specific criteria such as morphology of the local VEG, a short AV or VA intervals and a VEG that precede the onset (delta wave) of the QRS identified a successful site for RF ablation. When present the accessory pathway potential indicates a high chance of a successful ablation; however when not present did not decrease the chance of success