An Arrhythmia is an abnormal rhythm of the heart and is caused by problems with your heart's electrical system. The electrical impulses may happen too fast, too slowly, or erratically - causing the heart to beat too fast, too slowly, or erratically. There are two basic kinds of arrhythmias. Bradycardia is when the heart rate is too slow - less than 60 beats per minute. Tachycardia is when the heart rate is too fast - more than 100 beats per minute.