A 63-year-old woman with symptomatic premature ventricular contractions (PVCs) underwent electrophysiologic testing. The PVCs were suggested to originate from the infra-aortic valvular left ventricular outflow tract because the PVCs had S-waves in leads I, V5, and V6, and an R/S ratio >1 in lead V1. However, during some PVCs without S-waves, the ST segment had negative retrograde P-waves with a longer ventricularatrial (VA) interval. A Radiofrequency (RF) application in the left coronary cusp completely eliminated the PVCs, suggesting that negative retrograde P-waves might have been observed as pseudo S-waves during the PVCs. © 2007, The Authors.