JOHN BAVOSI / SCIENCE PHOTO LIBRARY JOHN BAVOSI / SCIENCE PHOTO LIBRARY
Cardiac arrhythmia. Illustration of a section through a human heart. Electrocardiogram (ECG) traces (red) show cardiac arrhythmia, the abnormal rhythm or rate of the heartbeat. Electrical impulses originate from the sinoatrial node (yellow, upper left). They then travel along the yellow neuromuscular fibres (green arrows show the direction of impulses) and stimulate contraction of the heart muscle fibres. Most impulses travel via the atrioventricular node (yellow, below sinatrial node). Cardiac arrhythmia is caused by a disturbance of these impulses, and usually results from disease or a drug overdose. The ECG traces allow accurate diagnosis.
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