What is the characteristic feature of a normal QRS complex on an ECG?

The characteristic feature of a normal QRS complex on an ECG is that it is narrow and typically lasts less than 0.12 seconds, which is less than half the duration of a large square (or block) on the ECG grid. This narrow shape indicates that the electrical impulse is effectively spreading through the ventricles, reflecting healthy conduction through the His-Purkinje system.

A normal QRS complex should not exhibit a wide duration, as that could suggest issues like bundle branch blocks or other forms of ventricular conduction delay. While amplitude can vary among individuals, a consistently high amplitude isn't a defining characteristic of a normal QRS; rather, what's more important is the duration and morphology of the complex on the ECG. Regularly timed intervals can be related to rhythm, but they do not specifically define the QRS complex itself, which is more about the shape and timing of the wave.