Some cells in adult animals do not appear to exhibit division (e.g., heart cell, nerve cell). These cell become inactive and become specialized by differentiate and do not further exit $\mathrm{G}_1$ phase, and enter a stage but divide occasionally called quiescent stage $\left(\mathrm{G}_0\right)$ of the cell-cycle.


Cell in this stage remain metabolically active but no longer proliferate unless called to do so depending on the requirement of the organism.