<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 . It corresponds to the depolarization of the right and left ventricles of the human heart . In adults, it 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 after 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> <P> Depolarization of the heart ventricles occurs almost simultaneously, via the Bundle of His and Purkinje fibers . If they are working efficiently, the QRS complex is 80 to 120 ms in duration . This is represented by three small squares or less at the standard paper speed of 25 mm / s . </P>

What is the heart doing during the qrs complex