The correct answer is option 3: Heart. A pacemaker is a small device that helps regulate the heartbeat. It is typically implanted in the chest, near the heart. The pacemaker sends electrical signals to the heart, prompting it to beat at a normal rhythm. This is particularly useful for individuals with irregular heartbeats (arrhythmias) or other heart conditions that affect the heart`s electrical system. The pacemaker acts as a backup system, ensuring that the heart continues to beat properly. It does not replace the heart, but rather, it assists in maintaining a steady and regular heartbeat. The liver, brain, and lungs do not have any direct association with pacemakers.