Answer: Option A
Step-by-step explanation: Pacemakers are artificial device used generates electrical signals in the heart. It is used when the heart is not able to contract and relax( pumping of blood) naturally. This is known as natural pacing of the heart.
This mechanism is controlled naturally by the sinoatrial node of the heart. When the muscles present in the heart relax and contract the pumping of blood takes place.
When this mechanism is not properly working, artificial devices called as pacemakers are used.