1. An instrument for recording the potential of the electrical currents that traverse the heart and initiate its contraction.
2. A device used for recording the electrical activity of the myocardium (heart muscle) to detect transmissions of the cardiac impulses through the conductive tissues of the muscle.

Electrocardiography allows for the diagnosis of specific cardiac abnormalities.

3. An instrument for recording the waveforms of voltages developed in the chest and lower parts of the human body in synchronism with the action of the heart.
4. An instrument used for making electrocardiograms.

I contains a lead-switching network, a differential amplifier, and a strip-chart recorder to trace the electrocardiogram on paper output.