The energy equation of a rigid sphere in a viscous fluid subject to an unsteady flow and temperature field is developed. A perturbation method is used to derive the heat transfer from a rigid sphere at low Peclet numbers. Thus, the temperature field is decomposed into the undisturbed field and the disturbance due to the presence of the sphere. A symmetry relationship is used to yield the rate of heat transfer due to the disturbance in the Laplace domain. The transformation of the rate of heat transfer in the time domain yields a history integral, which combines the effects of all past temperature changes of the sphere. This history integral in the energy equation is analogous to the history force (or Basset force) in the equation of motion of the sphere. By the heat-momentum transfer analogy, it is anticipated that the history term will play an important role in liquid-solid heat or mass transfer and that, depending on the frequency of the fluid temperature domain, it may account for up to 25% of the instantaneous heat transfer.