This electrocardiogram shows sinus rhythm and a Wolff-Parkinson-White, WPW, pattern of ventricular pre-excitation, due to an accessory pathway that bypasses de AV node to activate the ventricle abnormally early.

The characteristic features of WPW demonstrated here include a short PR interval, in this case, less than eighty milliseconds in, for example, lead I. A slurred or slow onset of the QRS, the the delta wave seen well in leads I, II and V4 through V7, where it is positive, and in leads aVR, V3R and V1, where it is negative. widening of the QRS interval, one hundred-twenty milliseconds in this example, and repolarization abnormalities with ST-T changes seen well in leads I and aVL. Note that the delta wave in this example simulates an anteroseptal infarction.