Why is the QRS complex larger than the P wave?

The QRS complex is larger than the P wave primarily because it represents ventricular depolarization, which involves a greater muscle mass compared to atrial depolarization that the P wave represents. The ventricles, being larger than the atria, generate a stronger electrical impulse when they depolarize, leading to a higher amplitude of the QRS complex. This increased electrical activity is evident in its size on an ECG, as more muscle fibers are activated during this phase.

In contrast, the P wave reflects the electrical activity of the atria, which are smaller chambers with less muscle mass than the ventricles. As a result, the amplitude of the electrical signal produced by the atria during depolarization is smaller, resulting in a smaller P wave. Therefore, the comparison of the sizes of these waves is significant as it indicates the respective muscle masses involved in the depolarization processes and helps in understanding the normal physiology of the heart.