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Heart pacemaker. Coloured chest X-ray showing a surgically-implanted heart pacemaker (at upper right). The two lungs appear white inside the ribcage bones, while the heart is the dark region at lower centre right. The pacemaker supplies electrical impulses along a lead (part of which is coiled) to the heart to keep it beating regularly. Pacemakers are fitted in patients with a malfunctioning sinoatrial node, the part of the heart which initiates each heartbeat, or in patients with a heart block which impairs the nerve impulses generated by the node. Heart pacemakers may provide a regular impulse or discharge only when a heartbeat is missed.
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