Electrocardiograph ECG is a test measures the electrical activity of the heart. Photo shows the manner in which the electrodes are attached to the patient, in this case, the hands and one foot being immersed in jars of salt solution.
Willem Einthoven was a Dutch doctor and physiologist. He invented the first practical electrocardiogram (ECG or EKG) in 1903 and received the Nobel Prize in Medicine in 1924 for it ("for the discovery of the mechanism of the electrocardiogram")