This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
QRS complex is due to 
Select and explain. 
A. Ventricular repolarization, B. Atrial depolarization, C. Conduction through AV node, D. Ventricular depolarization
D: Ventricular depolarization
Answer: D: Ventricular depolarization 
Explanation: P wave is primarily produced by atrial depolarization, the QRS complex is dominated by ventricular depolarization, and the T wave by ventricular repolarization. The U wave is an inconstant finding that may be due to ventricular myocytes with long action potentials. Ref: Ganong&;s Review of medical physiology 25th edition. Page: 522