  We study cascade decays of heavy neutral Higgs bosons through vectorlike
quarks. We focus on scenarios where decay modes into pairs of vectorlike quarks
are not kinematically open which extends the sensitivity of the LHC to larger
masses. Assuming only mixing with the third family of standard model quarks the
new decay modes of heavy Higgs bosons are: $H\to t_4 t \to Wbt, Zt t, ht t$ and
$H\to b_4 b \to Wtb, Zb b, hb b$, where $t_4$ ($b_4$) is the new up-type
(down-type) quark mass eigenstate. In the numerical analysis we assume the CP
even Higgs boson in the two Higgs doublet model type-II but the signatures are
relevant for many other scenarios. We identify the region of the parameter
space where these decay modes are significant or can even dominate, and thus
they provide the best opportunities for the simultaneous discovery of a new
Higgs boson and vectorlike quarks. We further explore the reach of the High
Luminosity LHC for two representative decay modes, $t_4\to Zt\to\ell\ell t$ and
$b_4\to Zb\to\ell\ell b$, and found that cross sections at a 0.1 fb level can
be probed with simple cut based analyses. We also find that the rates for Higgs
cascade decays can be much larger than the rates for a single production of
vectorlike quarks. Furthermore, the reach for vectorlike quarks in Higgs
cascade decays and pair production extends to comparable masses.
