ECG is the simplest  and the easily available tests that a heart patient can look for. This is an electrical recording of the heart. ECG reflects the proper functioning of the heart muscles and their condition as a function of the blood supply and oxygen received by them.

A single ECG curve has five main components - p, q, r, s, t. The space between s and t , called the ST segment can indicate angina, during the recording of the heart beating. ST segment lowering (medical term depression) is taken as a sure sign of angina. T wave inversion is also a sign of Angina.

One must realise a doctor has to get a training of more than five years to analyse the ECG, even then it may be difficult for him to know everything about ECG. It is advisable that a final decision should be taken only after the ECG is seen by a qualified doctor.

ECG is a simple and convenient investigation which can be done at the bed side to observe angina. 

Breathlessness is felt, if ECG changes appear early in the TMT, then the coronary heart disease is severe, and if the changes appear later they are not so severe.