  We prove sharp geometric rigidity estimates for isometries on Heisenberg
groups. Our main result asserts that every $(1+\varepsilon)$-quasi-isometry on
a John domain of the Heisenberg group $\mathbb{H}^n$, $n>1$, is close to some
isometry up to proximity order $\sqrt{\varepsilon}+\varepsilon$ in the uniform
norm, and up to proximity order $\varepsilon$ in the $L_p^1$-norm. We give
examples showing the asymptotic sharpness of our results.
