  In this paper, we study transition density functions for pure jump unimodal
L\'evy processes killed upon leaving an open set $D$. Under some mild
assumptions on the L\'evy density, we establish two-sided Dirichlet heat kernel
estimates when the open set $D$ is $C^{1, 1}$. Our result covers the case that
the L\'evy densities of unimodal L\'evy processes are regularly varying
functions whose indices are equal to the Euclidean dimension. This is the first
results on two-sided Dirichlet heat kernel estimates for L\'evy processes such
that the weak lower scaling index of the L\'evy densities is not necessarily
strictly bigger than the Euclidean dimension.
