Time‐ and energy‐resolvedd‐3He fusion reactions have been measured to infer the energy of thed+or He++minority ions heated near their cyclotron frequency by the magnetosonic fast wave. The average energy of the reacting3He ions during3He minority heating is in the range of 100–400 keV, as deduced from the magnitude of the reaction rate, its decay time, and the energy spread of the proton reaction products. The observed reaction rate and its scaling with wave power and electron density and temperature are in qualitative agreement with a radial reaction rate model using the minority distribution predicted from quasilinear velocity space diffusion. Oscillations in the reaction rate are observed concurrent with sawtooth andm=2 magnetohydrodynamic activity in the plasma.