a heart murmur
is NOT an irregular heart beat at all. The heart has four valves use to separate the four chambers of the heart from each other. At different points during a heat beat different valves open and close to allow the blood to only travel in a forwards (not a reverse) direction. A murmur occurs (usually, not always, there are other causes) because of a problem with one of the valves. The valve could be failing to close fully, causing a regurgitant murmur from the leak. Alternatively, the valve could be obstructed or failing to open all the way, causing a stenotic murmur.