Hi welcome to HCM. The most serious causes of chest pain are an attack of myocardial infarction
) and pulmonary embolism
( block in a lung artery
). Both these conditions can be diagnosed by an ECG. And if it is not done, these serious conditions can sometimes be missed leading to even fatality.
Also it is sometimes impossible to clinically differentiate between an attack of heart burn (acidity) and a heart attack both of which lead to chest pain. Therefore in every case of moderate and severe chest pain
it is advisable and in the patient's interest to take an ECG. That is why doctors do so.
Hope this answers your query fully.