hi and pleased to answer you The ST segment is the time between the terminal contraction of the ventricle and the beginning of the relaxation of the ventricle, on EKG, it’s the area between the end of the QRS complex and the start of the T-wave which follows the QRS complex. When there are symptomatic heart diseases, the types of abnormalities are varied and include ST segment depression or elevation, flattening of the T wave, biphasic T waves, or T wave inversion. Significant ST segment depression usually means that there is significant diminution of the coronary blood flow conditioning myocardial ischemia but flow still exist (low blood flow) in the heart. Significant ST segment elevation means a total blood flow obstruction and there has been an acute infarction of heart muscle. ST segment changes without symptoms (chest pain, shortness of breath, exercise intolerance, …etc.) means absolutely nothing bad for your health, but should prompt further investigations. ST segment changes can range from being an important tool diagnosing underlying diseases to a variant of EKG normality, and may be seen in any lead of the electrocardiogram. Factors affecting the ST-T configuration may include, intrinsic myocardial disease (ischemia, infarction, myocarditis), Drugs (digoxin, quinidine, etc..), Ions electrolyte abnormalities, neurogenic factors (stroke, trauma, tumor, etc.), metabolic factors (diabetes, etc..), Atrial electric abnormalities (fast heart rates the atrial T wave may pull down the beginning of the ST segment), ventricular conduction abnormalities and rhythms originating in the ventricles. your cardiologist is right may this answer help you and best wishes.