The pacemaker helps the arrythmias of the human heart. The arrythmias is a problem with the rythme and the rate of the heartbeat. The sensors called electrodes are in the pacemaker which helps monitor and control your heartbeat. The electrodes feel your hearts activity and send data through the wires and back to the computer. If your heart has not got a good rhythm the computer directs the generator to send electrical pulses through the wires and into the heart.

Here's a light hearted look at pacemakers.