Heat generation in steel samples with discontinuity-like defects subjected to tensile loading is analyzed by using the technique of infrared thermography. It is shown that the heat is predominantly generated in shear bands where one observes a considerable rise in temperature. The sample mean temperature is conditioned by the sum of all heat sources (shear bands), as well as the thermal properties of the material and the magnitude of the heat exchange with the environment. It also depends on the mass of elastically deformed material adjacent to the shear bands.