A normal ECG comprises of three recognizable waves:
- P wave: represents the depolarization of the atria
- QRS complex: represents the depolarization of the ventricles. In this stage the electrical signal travels from the endocardium to the epicardium of the ventricles.
- T wave: this represents the repolarization of the ventricles. This travels from the epicardium of the ventricles towards the endocardium of the ventricles.
Between the QRS-complex and the T wave, there is an interval called the ST segment. This interval normally takes about 5-150 ms on an ECG. It represents the isoelectric period of the ventricles; this is the time between depolarization and repolarization.