Electrocardiography electrodes placed at specific points on a 45-year-old man's chest. This is part of an electrocardiography (ECG) examination to check the health of the patient's heart, a fist- sized organ that lies below the middle two electrodes. The heart is a hollow muscular organ that pumps blood around the body. The muscular activity is produced by a rhythmic electrical activity, which is being recorded by these electrodes. Twelve electrodes are used in an ECG examination (four of the six chest electrodes are seen here). The examination can help diagnose a range of heart complaints. Photographed at the American Hospital of Paris, France.