The invention discloses an electrocardiogram teaching aid which comprises a heart model, a heart support and a light source system. The heart model is marked with a heart depolarization direction; theheart support comprises a support member for supporting the heart model as well as a face panel and a horizontal plane panel vertical each other, the side, close to the heart model, of the face panelincludes a face panel lead coordinate marked with scales, and the side , close to the heart model, of the horizontal plane panel includes a horizontal plane lead coordinate marked with scales; and the light source system comprise a face panel parallel light source and a horizontal plane parallel light source. Via the electrocardiogram teaching aid, the magnitudes of depolarization electrocardio vectors of different leads in the depolarization process of the heart can be measured in a simulated way and explained visually, and further the spatial positions, sizes of ventricles and electrocardioactivities of the heart can be explained according to electrocardiogram graphs, and teaching of the electrocardiogram principle is more visual and easier to understand.