This work shows an experimental study accomplished on a cylindrical resonant cavity, inside of which, through a tube concentric to it, fluids flow. Inside the cavity is inserted microwave power, whose aim is to heat the flowing fluid. It s not trivial to foresee the electric field distribution inside a resonant cavity. Its geometric shape, together with several parameters, and the material in it inserted to absorb microwave power are variables that influence on the intensity and electromagnetic field distribution inside de cavity. Therefore, to heat samples whose dimensions don’t allow the absorption degree of energy through perturbation theory in cavities to be analyzed, it is necessary to verify both experimentally and theoretically all the process on study. The objective of this work is to analyze the influences of disturbances inside a cavity, seeking the practical possibility of heating optimization of the fluids inside of it. Such modification consists of three metallic stems placed on a transversal section of the cavity, besides the variation of the tubes external diameter where the fluid to be heated will flow. The cavitie s study, seeking for the optimization of the heating inside of it, has a result less waste of applied energy on these heating systems.