QRS Complex & Ventricular Depolarisation — NEET Biology

The QRS complex on an ECG represents the electrical depolarisation of the ventricles, which triggers ventricular muscle contraction and marks the start of systole. Students often confuse QRS with atrial activity or mistake it as repolarisation instead of depolarisation. The key distinction: Q-R-S together specifically show ventricular depolarisation, NOT atrial events (that's P wave). Remember that depolarisation precedes contraction—QRS comes first, then mechanical contraction follows. This is frequently tested because understanding ECG waves directly links to cardiac physiology and pressure changes during the cardiac cycle.