Electrocardiogram (ECG) strips showing loss of preexcitation with exercise in person with the Wolff-Parkinson-White (WPW) pattern

Leads aVF, V1, and V5 from the surface ECG of a patient with Wolff-Parkinson-White pattern and a right anterior accessory pathway. Prior to exercise, the resting ECG shows preexcitation with a short PR interval, delta wave, and prolonged QRS interval. With exercise and a heart rate of 130 beats per minute, there is abrupt loss of preexcitation: the PR interval lengthens, the delta wave disappears, and the QRS complex morphology normalizes.