In this talk, after reviewing the basics of the massive spinor helicity formalism, we introduce a momentum shift based on the helicity basis. This momentum shift allows an on-shell reconstruction of renormalizable theories with particles of any mass. As a demonstration of our method, we compute $e^+ e^- \to \mu^+ \mu^-$ and $W^+W^- \to W^+W^ $ amplitudes. An issue was raised on the former amplitude in literature and we see that, with our momentum shift, we can resolve the issue. In the latter case, we recover the correct amplitude, which contains the four-point contact interaction in terms of the Feynman diagrams, solely from the three-point amplitude. We see that this result is closely related to the Ward identity.