Shown on this slide is an example of the signals monitored in an ECG. In the diagram on the left is a typical ECG waveform showing the atrial depolarization and the ventricular depolarization, which is represented by that large QRS interval. On the right is an illustration showing each portion of the heart and the signal that it contributes to the overall ECG waveform. In the top portion the ECG waveform starts at the spinal atrial node and progresses through the atrial muscle, then through the AV node all the way down through the left ventricle, which is the portion of the heart that is responsible for pumping blood throughout the body. The point of this is that by knowing what a normal ECG waveform looks like, it is possible to evaluate an abnormal waveform and allows a cardiologist to diagnose arrhythmias and locate them in specific areas of the heart.