An ECG is an abbreviation for Electrocardiogram. The instrument used to make an ECG is an electrocardiograph. This machine records electrical activity in the body, especially the heart.
The heart receives tiny electrical signals from the nerves. These signals tell the heart to pump blood throughout the body. An ECG machine has electrodes that are attached to different parts of the body. The electrodes detect the tiny electrical signals and draw a graph. The graph tells the doctor whether or not the heart is functioning normally.
The electrocardiograph was developed from the string galvanometer invented by the Dutch physiologist, Willem Einthoven who was awarded the Nobel Prize in 1924.