It is a graphical representation of the electrical activity of the heart during a single cardiac cycle. The electrocardiogram is obtained by a machine known as an electrocardiograph. The study or the process of recording of the electrocardiogram is called electrocardiography.
Einthoven (1903) is known as 'father of electrocardiography'.
The impulse generated by the SA node causes contraction and relaxation of heart chambers. To obtain an ECG, a patient is connected to the machine with three electrical leads (i.e., one to each wrist and one to the left ankle), monitoring the activity of the heart continuously and heart's functioning is evaluated by attaching multiple leads to the chest region.