Healing Non-Regenerative Tissue

[KI1]

I know that nervous cells are permanently in the G₀ phase of the cell cycle and that the only way that they can regenerate is by recreating their axons and dendrites to reform connections. But how do other non-regenerative tissues work? As far as I know, the heart does not regenerate itself through cells going through mitosis? How then does the heart become stronger? And why would the heart need a reservoir of stem cells as some research has shown? And if heart cells do go through mitosis, how can they connect to the already working machine of the heart while everything is moving and working? These questions can also be applied to the lungs too because they never stop either.