ECG qtc prolongation, also called QTc interval prolongation, indicates that the cardiac depolarization and repolarization time is delayed beyond the normal range, resulting in a variety of causes, usually seen in the clinic in congenital diseases, cardiac diseases, electrolyte disorders, drug effects. 1. Congenital diseases: Long QT interval prolongation syndrome is usually congenital and often familial. 2. Heart disease: such as heart failure, rheumatic heart disease, coronary artery insufficiency, myocarditis and other myocardial injury diseases. 3. Electrolyte disorders: hypokalemia, hypomagnesemia, hypocalcemia can lead to prolongation of QTc on ECG. 4. Drug effects: common as antiarrhythmic drugs, sedative drugs, tricyclic antidepressants can cause ECG QTc prolongation. QTc prolongation of electrocardiogram is an abnormal manifestation of electrocardiogram, if found, you need to go to the hospital specialist for further examination, clear diagnosis, do not blindly self-medication, so as not to cause adverse consequences and delay the condition.