It is a well known fact that the human heart uses electrical currents in order to keep the cardiac muscles pumping in time. The current it taken to the muscle cells by conducting cells which pass the current through the heart to the correct places. The sinoatrial node is the originator of the signal which then moves to activate the atria and then the ventricles.
Now I actually have been diagnosed with having first degree heart block, which is so minor it doesn’t even cause noticeable bradycardia (slowing of heart beat). This means that the due to a lack of conductivity in my heart there is a slight delay between the contraction of the atria and the ventricles although not enough to have any noticeable adverse effects. For others though, it can be a lot more serious. Cardiovascular diseased cause the highest number of deaths in the world according to the World Health Organisation (WHO?), with many of these being caused by arrhythmias.