Electrocardiography (ECG) is a method of examining the contraction and relaxation stages of the atria and ventricles of the heart, and printing the electrical activity that occurs during the stimulation of the heart and transmitting the stimulus on millimetric paper.

In this method, a complex consisting of P, Q, R, S, T and U waves, corresponding to each heartbeat, is seen.

Irregularities in these waves give doctors clues about heart disease.

ECG is usually taken when:
1. People with chest pain (especially for investigating coronary artery disease)
2. In people who describe palpitations and dizziness
3. For differentiation of lung disease, heart failure in people with shortness of breath
4. Persons without significant discomfort (for screening or preoperative examination)
5. To investigate the side effects of drugs used