Arrhythmia is the medical term for an irregular heartbeat or abnormal heart rhythm.There are basically two main things that can go wrong with the heart: plumbing and electrical. Many of us are acutely aware of plumbing problems in the heart, but we are still mostly unaware of the electrical faults that cause arrhythmias. Arrhythmias can occur in the upper chambers of the heart (atria) or in the lower chambers of the heart (ventricles). Arrhythmias can occur at any age. Some are barely detectable, while others can be more dramatic and may even lead to sudden cardiac death.