FAULTY HEART BEAT – ARRYTHMIA – By Dr. Gnana Sankaralingam It is electricity that makes the heart to beat. Heart has an inbuilt electrical system that ensures the orderly contraction of its two upper chambers, the atria which pump blood into the lower chambers the ventricles, which in turn contract and push out blood. All these take less than a second. Starting point for this is the natural pacemaker known as sino-atrial (SA) node, a collection of cells located in upper right atrium, whose activity is controlled by nerves from the brain: sympathetic to trigger it and parasympathetic acting as a brake. Both act to regulate the rhythm, so that heart contracts at 60 to 100 beats a minute. SA node acts like a spark plug, spontaneously producing an electrical signal which it sends through a network of wires which are modified nerve cells, to all four chambers of ...