MODEL RELEASED. Heart pacemaker surgery. Image 8 of 9. Close-up of electrical wires for a pacemaker in a patient's chest. The wires have been inserted via an incision just below the collar bone (clavicle) into an artery and then down into the heart. A pacemaker is a device that supplies electrical impulses to the heart to keep it beating regularly. The main body of the pacemaker sits just under the skin and is attached to the wires. This pacemaker is being fitted to treat a heart block. This condition impairs the nerve impulses created by the sinoatrial node, the part of the heart that initiates the heartbeat. For a sequence showing the operation see M560/596 to M560/604.