Effects of heavy fields during inflation will be discussed. Inflationary models based on high energy theories, such as supergravity and superstring theory, generically contain heavy scalar fields in addition to the inflaton. Such heavy scalar fields could be therefore used as a probe of high energy physics. In this talk, I will discuss multi-field inflation models with a turning background trajectory, as a possible scenario heavy fields can affect inflationary dynamics. When heavy fields are excited after the turn and oscillate around the bottom of the potential, the following two effects are generically induced: deformation of the inflationary background spacetime and conversion interactions between adiabatic and isocurvature perturbations. I will discuss such effects on primordial power spectra of curvature perturbations.