Catheter ablation of ventricular tachycardia (VT) depends on the localization of VT circuit. Late potential (LP) recordings in sinus rhythm suggest slow conduction and may help to identify the reentry circuit. Detailed entrainment mapping was performed to identify VT circuits in 15 patients with structural heart disease. LPs were identified during baseline non-VT rhythm and were defined as electrogram signals occurring beyond the end of surface QRS. The QRS-LP interval was measured from onset of QRS to the latest LP component. Entrainment was performed in 21 VTs, of which three entrance, 13 isthmus, 17 exit, and one outer loop sites were identified (n = 34). Bipolar electrograms (n = 133 sites) at and in proximity (<1.5 cm distance) to the VT circuit were analyzed. A higher incidence of LP was recorded near isthmus (89%) compared to entrance (57%) or exit (20%), p < 0.05. The QRS-LP intervals were markedly longer at entrance (218 +/- 27 ms) and isthmus (194 +/- 40 ms) compared to those recorded at exit (131 +/- 29 ms), p < 0.05. Electrograms near the VT circuit isthmus have a higher incidence of LP compared to that of entrance and exit; and the QRS-LP interval is significantly longer near entrance and isthmus compared to exit sites. These findings have important implications in substrate-based ablation strategies targeting LPs.