  We investigate, within the type-II two-Higgs-doublet extension of the
standard model (SM), the impact of heavy neutral Higgs boson resonances with
unsuppressed Yukawa couplings to top quarks on top-quark pair production at the
LHC at next-to-leading order (NLO) in the strong coupling constant. We take
into account the resonant Higgs boson contributions, the non-resonant SM
$t\bar{t}$ continuum and the interference of these two contributions. The NLO
QCD corrections to heavy Higgs production and the interference contributions
are calculated in the large top-quark mass ($m_t$) limit, including an
effective K-factor rescaling. Our evaluation of the QCD-Higgs interference is
focused on the Higgs resonance region. Using representative CP-conserving as
well as CP-violating parameter scenarios phenomenological results are presented
for different observables.
