| RR Interval | The interval between an R wave and the next R wave: Normal resting heart rate is between 60 and 100 bpm. | 0.6 to 1.2s |
| P Wave | During normal atrial depolarization, the main electrical vector is directed from SA node towards the AV node, and spreads from the right atrium to the left atrium. This turns into the P wave on the ECG. | 80m s |
| PR Interval | The PR interval is measured from the start of P wave to the start of the QRS complex. | 120 to 200ms |
| PR Segment | The PR segment connects P wave and QRS complex. The impulse vector is from the AV node to bundle branches and then to the Purkinje fibers. | 50 to 120ms |
| QRS Complex | The QRS complex reflects the rapid depolarization of the right and the left ventricles. They have a large muscle mass compared to atria, so the QRS complex usually has much larger amplitude than the P-wave. | 80 to 120ms |
| ST Segment | The ST segment connects the QRS complex and T wave. The ST segment represents the period when ventricles are depolarized. It is isoelectric. | 80 to 120ms |
| T Wave | The T wave represents the repolarization (or recovery) of ventricles. The interval from the beginning of QRS complex to the apex of the T wave is referred to as the absolute refractory period. | 160ms |
| ST Interval | It represents the interval between ventricular depolarization and repolarization. | 320ms |
| QT Interval | The QT interval is measured from the beginning of the QRS complex to end of the T wave. | Up to 420ms in heart rate of 60 bpm |