The electrical cardiac axis, also known as the mean electrical axis, usually refers to the average direction of the heart’s electrical activity. A leftward deviation of 79.9 of the cardiac electrical axis is a leftward deviation of 79.9 degrees of the heart’s electrical activity. The electrical cardiac axis is generally defined as the angle formed by the all-instantaneous maximum integrated vector of the ventricles during depolarization and repolarization with respect to the horizontal axis. It is generally a measurement of the mean QRS electrical axis, and the normal cardiac electrical axis ranges from plus -30 to +90 degrees. Leftward deviation of the ECG axis is usually seen when the electrical impulse is blocked in the left anterior branch, and also when the position of the heart in the thoracic cavity is to the left, which also affects the ECG axis. If the leftward deviation of ECG is 79.9 degrees, it is recommended to consult a doctor for further examination to identify the cause of the deviation and to carry out targeted treatment or therapy.