An electrical axis of +30° to -30° is a mild leftward deviation of the electrical axis and is common in normal transverse hearts (obesity, ascites, pregnancy, etc.), left ventricular hypertrophy, and left anterior branch block. The electrical axis is an electrocardiographic term that refers to the combined direction of the electrical vectors generated by the depolarization of the heart. The doctor measures the ECG to obtain the exact value of the cardiac axis. The normal ECG axis is located at -30° to +90°. +90° to +180° is right deviation, -30° to -90° is left deviation, and +30° to -30° is mild left deviation. Mild left deviation of the ECG electrical axis is commonly due to physiologic reasons, related to body size, position of the heart, etc., and does not require much intervention or treatment. Pathologic causes such as left heart enlargement, left ventricular hypertrophy, hypertension or cardiomyopathy should be treated actively. Echocardiography can be performed to clarify whether there is left deviation of the electrical axis due to left heart enlargement or left ventricular hypertrophy. In general, a mild leftward deviation of the electrical axis on the ECG is not a cause for concern. It is not necessary to treat the leftward deviation of the electrical axis itself, and the main purpose is to actively treat and control the primary cause of the disease.