Atrial fibrillation (AF) is an abnormal heart rhythm. The heartbeat is irregular and often fast. It is the most common heart rhythm disorder in the UK affecting one per cent (one in 100) of the population under 65 years old and ten per cent (one in ten) of patients aged over 75 years. Patients with AF may have no complaints or symptoms, such as palpitations, shortness of breath, lack of energy, light-headedness and chest discomfort. Some patients with AF may even develop evidence of heart failure or suffer a stroke.