The Heart crack on the tongue is relatively common. This crack is in the midline extending from near the root to near the tip; it therefore extends nearly the whole length of the tongue. The Heart crack indicates the constitutional tendency to mental-emotional problems: the deeper the crack, the stronger this tendency. If the Heart crack is accompanied by a change in the tongue-body colour and a red tip, it then indicates actual mental-emotional problems.
The two tongues presented here both have a Heart crack. The worst is the one on the bottom because the crack is deeper.