An electrocardiogram (ECG or EKG) is a test that measures the electrical activity of the heart. The accompanying photo illustrates how electrodes are attached to the patient, with the hands and one foot immersed in jars of salt solution. Willem Einthoven was a Dutch doctor and physiologist who invented the first practical electrocardiogram in 1903. He was awarded the Nobel Prize in Medicine in 1924 for his work, specifically for the discovery of the mechanism of the electrocardiogram.