Heart pacemaker. Coloured frontal X-ray of the chest of a patient with a heart pacemaker (centre left). The heart is at lower right, the two dark areas on either side are the lungs. The pacemaker supplies electrical impulses, along a lead, to the heart to keep it beating regularly. Pacemakers are fitted in patients with a malfunctioning sinoatrial node, the part of the heart that initiates the heartbeat, or in patients with a heart block, which impairs the nerve impulses generated by the node. Pacemakers may provide a regular impulse or discharge only when a heartbeat is missed.
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