A star like Sun is in a state of an equilibrium between gravitational forces that want to collapse the star and the fusion energy. Gravitational pressure helps atoms to collide and fusion takes place. But it doesn't sound right to say that the heat is from the pressure.
Once the fusion energy isn't enough to counteract the gravity, the star collapses into a white dwarf (or a super-nova later).
Once the fusion energy isn't enough to counteract the gravity, the star collapses into a white dwarf (or a super-nova later).
https://en.wikipedia.org/wiki/Main_sequence