A first degree heart block is hardly noticeable to the naked eye. A second degree heart block is one in which the heart does not depolarize. A third degree heart block is very significant. It is noticed on a ECG by no real association with p waves and QRS complexes. These blocks require pacemaker implimentation.
Ventricular fibrillations are the most serious.
In ventricular fibrillations, the blood is not being propelled effectively at all. This can lead to a loss of conciousness in seconds. They are noticed on a ECG by total random spikes and no P waves. Arrythmias are important to understand because it can save someones life. Arrythmias can be clues into poor health.