DR P. MARAZZI / SCIENCE PHOTO LIBRARY DR P. MARAZZI / SCIENCE PHOTO LIBRARY
Healthy heart. Electrocardiogram (ECG) traces showing the healthy heartbeat of a 32-year-old man. An ECG measures the pumping of the chambers of the heart via 12 external electrodes (I-III, V1-6, aVR, aVL and aVF) and records them as electrical waves (white), one for each electrode. The tall peak and trough complexes (for example in the V4 trace) represent the contraction of the lower heart chambers (ventricles). The smaller waves just before the peaks show the upper chambers (atria) contracting. ECG traces are important for the diagnosis of heart disease. They can reveal the location and nature of many cardiac disorders.
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