How relevant are top loops in VBS at the LHC?

We present the contributions to the imaginary part of the $W^{+}{W}^{-}$ elastic scattering from top and bottom quark one-loop diagrams. The computation is performed within the context of HEFT, where we compare them with the boson-loop corrections. We argue that the often neglected (top and bottom) fermion contributions may in fact be relevant.