The use of the electrical analogy in heat transfer allows to simply solve many problems in various fields such as building or electrothermics.Nevertheless, it is limited to systems with two isotherms and a flux tube. The fin approximation allows to introduce an exchange on the flux tube, but the electrical analogy does not work anymore if there is a heat source inside the fin. In this paper, we will construct an electrical analogy for a system with:- On its boundary, several isotherms surfaces, a surface that exchanges with the external medium and a zero flux region,- In the volume, a heat source with any distribution.This approach generalizes the notions of thermal resistance and partition coefficient of the internal heat source.In the applications (here for a cylinder), the only approximation concerns the isotherms surfaces which in reality are not necessarily so (this approximation already exists in the elementary case, a thermal resistance is defined between two isotherms).