<P> The QRS complex is a name for the combination of three of the graphical deflections seen on a typical electrocardiogram (EKG or ECG). It is usually the central and most visually obvious part of the tracing, in other words, it's the main spike seen on an ECG line . It corresponds to the depolarization of the right and left ventricles of the human heart and contraction of the large ventricular muscles . </P> <P> In adults, the QRS complex normally lasts 0.06--0.10 s; in children and during physical activity, it may be shorter . The Q, R, and S waves occur in rapid succession, do not all appear in all leads, and reflect a single event and thus are usually considered together . A Q wave is any downward deflection immediately following the P wave . An R wave follows as an upward deflection, and the S wave is any downward deflection after the R wave . The T wave follows the S wave, and in some cases, an additional U wave follows the T wave . </P>

What does the electrocardiogram (ecg) qrs wave indicate is happening in the heart