  The non-decoupling effects of heavy Higgs bosons as well as fermions on the
loop-induced $H^\pm W^\mp Z^0$ vertex are discussed in the general two Higgs
doublet model. The decay width of the process $H^+ \to W^+ Z^0$ is calculated
at one-loop level and the possibility of its enhancement is explored both
analytically and numerically. We find that the novel enhancement of the decay
width can be realized by the Higgs non-decoupling effects with large
mass-splitting between the charged Higgs boson and the CP-odd one. This is due
to the large breakdown of the custodial $SU(2)_V$ invariance in the Higgs
sector. The branching ratio can amount to $10^{-2} \sim 10^{-1}$ for $m_{H^\pm}
= 300$ GeV within the constraint from the present experimental data. Hence this
mode may be detectable at LHC or future $e^+e^-$ linear colliders.
