A disorder characterized by an electrocardiographic finding of a supraventricular arrhythmia characterized by the replacement of consistent P waves by rapid oscillations or fibrillatory waves that vary in size, shape and timing and are accompanied by an irregular ventricular response. (CDISC). The disease is atrial fibrillation (MONDO_0004981). Also known as: A-fib, AF, AFib, atrial fibrillation (disease).