  The recent time witnessed a surge of interest in strong gravitational lensing
by black holes is due to the Event Horizon Telescope (EHT) results, which
suggest comparing the black hole lensing in both general relativity and
heterotic string theory. That may help us to assess the phenomenological
differences between these models. Motivated by this, we consider gravitational
lensing by the nonsingular Kerr-Sen black holes, which encompass Kerr black
holes as a particular case, to calculate the light deflection coefficients $p$
and $q$ in strong-field limits, while the former increases with increasing
parameters $k$ and charge $b$, later decrease. We also find a decrease in the
light deflection angle $\alpha_D$, angular position $\theta_{\infty}$ decreases
more slowly and impact parameter for photon orbits $u_{m}$ more quickly, but
angular separation $s$ increases more rapidly with parameters $b$ and $k$. We
compare our results with those for Kerr black holes, and also the formalism is
applied to discuss the astrophysical consequences in the case of the
supermassive black holes NGC 4649, NGC 1332, Sgr A* and M87*. In turn, we also
investigate the shadows of the nonsingular Kerr-Sen black holes and show that
they are smaller and more distorted than the corresponding Kerr black holes and
nonsingular Kerr black holes shadows. The inferred circularity deviation
$\Delta C\leq 0.10$, for the M87* black hole shadow, put constraints on the
nonsingular Kerr-Sen black hole parameters ($a, k$) and ($a, b$). The maximum
shadow angular diameter for $b=0.30M$ and $k=0.30M$ are, respectively,
$\theta_d=35.3461\,\mu$as and $\theta_d=35.3355\,\mu$as. We also estimate the
parameters associated with nonsingular Kerr-Sen black holes using the shadow
observables.
