ECG shows left deviation, meaning that the cardiac axis is between -30° and -90°. It may occur in physiological conditions or may be seen in pathologic diseases. The former is mainly related to body size and development, while the latter is commonly seen in coronary artery disease, myocardial hypertrophy, myocarditis, and so on. The electrocardiogram (ECG) shows that the normal electrical axis of the heart is between 0° and +90°, but if the measured electrical axis is between 0° and -90°, the electrical axis is left deviation, which may be seen in physiological conditions, such as short and fat body type, or may be related to developmental abnormality, such as leftward development of the heart, and leftward deviation of the electrical axis is often seen in the elderly. However, leftward deviation of the electrical axis is more common in pathologic conditions, such as hypertensive heart disease, coronary artery disease, myocarditis, etc. These diseases can cause left ventricular hypertrophy. These diseases can lead to left ventricular hypertrophy and may damage the left anterior branch of the heart’s electrical conduction pathway, thus causing leftward deviation of the electrical axis. If it is caused by physiological factors, it does not need special treatment. If it is caused by pathological factors, it needs to be actively treated for the primary disease. If the physical examination reveals abnormal ECG, it is recommended to consult a doctor in time to avoid delaying the condition.