S wave
Also calledS-wave
Definition
A negative (downward) deflection of the QRS complex that follows an R wave. It is normally deepest in the right precordial leads and becomes smaller across the precordium, often disappearing in V5 and V6, as the R wave grows. The Sokolow-Lyon criterion for left ventricular hypertrophy is met when the S wave in V1 plus the R wave in V5 or V6 is 35 mm or more.
Sources
- Hancock EW, Deal BJ, Mirvis DM, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part V: electrocardiogram changes associated with cardiac chamber hypertrophy. Circulation. 2009;119(10):e251-e261. doi.org/10.1161/CIRCULATIONAHA.108.191097
- Samesima N, God EG, Kruse JCL, et al. Brazilian Society of Cardiology guidelines on the analysis and issuance of electrocardiographic reports - 2022. Arq Bras Cardiol. 2022;119(4):638-680. doi.org/10.36660/abc.20220623
- Meek S, Morris F. ABC of clinical electrocardiography. Introduction. II: Basic terminology. BMJ. 2002;324(7335):470-473. doi.org/10.1136/bmj.324.7335.470
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.