The delta wave ECG refers to a unique waveform seen on an electrocardiogram, characterized by a slurred upstroke in the QRS complex. It is most commonly associated with Wolff-Parkinson-White (WPW) syndrome, a condition where an extra electrical pathway in the heart leads to rapid heart rates. In essence, the delta wave represents an abnormal conduction pathway, causing a premature activation of the ventricles. When interpreting the delta wave ECG, it is crucial to recognize that this waveform alters the standard appearance of the QRS complex. The delta wave can lead to a short PR interval and a widened QRS complex, both of which are key diagnostic criteria for WPW syndrome.