Whether cell forces or extracellular matrix (ECM) can impact genome integrity is largely unclear. Here， acute perturbations (～1 h) to actomyosin stress or ECM elasticity cause rapid and reversible changes in lamin-A， DNA damage， and cell cycle. The findings are especially relevant to organs such as the heart because DNA damage permanently arrests cardiomyocyte proliferation shortly after birth and thereby eliminates regeneration after injury including heart attack. Embryonic hearts， cardiac-differentiated iPS cells (induced pluripotent stem cells)， and various nonmuscle cell types all?show that actomyosin-driven nuclear rupture causes cytoplasmic mis-localization of DNA repair factors and excess DNA damage. Binucleation and micronuclei increase as telomeres shorten， which all favor cell-cycle arrest. Deficiencies in lamin-A and repair factors exacerbate these effects， but lamin-A-associated defects are rescued by repair factor overexpression and also by contractility modulators in clinical trials. Contractile cells on stiff ECM normally exhibit low phosphorylation and slow degradation of lamin-A by matrix-metalloprotease-2 (MMP2)， and inhibition of this lamin-A turnover and also actomyosin contractility are seen to minimize DNA damage. Lamin-A is thus stress stabilized to mechano-protect the genome.