Electrical stimulation is required for heart muscle to contract. The right atrium of the heart has cells that regularly outputs electrical stimuli. This electrical stimulus must spread all over the heart. The heart has lines consisted of sequentially located cells that the electricity flows through, as in an electrical grid. And the cardiac muscle responds to this electrical stimulus. Any abnormality in these structures results in the disruption of heart rhythm.
Arrhythmia exhibits itself in the form acceleration (tachycardia), irregular beat (premature beat) or decelaration (bradycardia).