DR P. MARAZZI / SCIENCE PHOTO LIBRARY DR P. MARAZZI / SCIENCE PHOTO LIBRARY
Pacemaker. Heart pacemaker 3 days after being implanted under the skin below the collarbone of a 77-year-old man. The lump in the skin is made by the battery unit. From this a wire runs to the heart (unseen). Black sutures (stitches) have closed up the surgical cuts made during implantation. Pacemakers supply electrical impulses to the heart to maintain a regular heartbeat. They are needed by patients with heart block, a condition in which the heart's natural pacemaker (sinoatrial node) fails to work properly. Depending on requirements, pacemakers can work constantly at a fixed rate or only discharge when the heart slows or misses a beat.
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