JOHN BAVOSI / SCIENCE PHOTO LIBRARY JOHN BAVOSI / SCIENCE PHOTO LIBRARY
Heart nerve conduction. Illustration of a section through a human heart with an electrocardiogram (ECG) trace. The heart is a hollow muscle that pumps blood around the body. ECG traces show the pumping of the heart as a series of waves caused by the electrical impulses that coordinate heart muscle contraction. The impulse starts at the oval sinoatrial node (yellow, at upper left) causing the two small upper heart chambers (atria) to contract. The impulse then runs down the nerve fibres (yellow) to the oval atrioventricular node (green, at upper centre). The two large lower heart chambers (ventricles, dark pink) then contract. ECG is vital for heart monitoring.
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