An arrhythmia is a disturbance of the heart's rhythm. An arrhythmia may result in a fast or slow heartbeat and/or produce an even or uneven rhythm. Two common arrhythmias arising from the atria are paroxysmal atrial tachycardia and atrial fibrillation. PAT often occurs in young, healthy individuals without heart disease. The heart beats at a rate of 150 to 250 beats per minute (BPM) rather than the normal 60 to 100 BPM. Despite the fast beating, individuals usually feel fine because they are young and healthy.