High carbon steel wires are largely used in structural applications such as reinforcement, bridge cables, steel ropes, etc. These applications require safety, reliability and durability, which implies in a constant effort to optimize and control the microstructure. The correct managing of the different steps of heat treatments is essential to achieve these aims. To address this problem, this study brings a critical investigation of the heating, from room temperature to austenitizing temperature, and cooling, from the austenitic domain to room temperature, of an eutectoid steel wire. Dilatometry with strict control of heating and cooling rates was employed to measure the variations in length in order to detect the minor changes in the microstructure and to explore the phase transformation features. The microstructure investigation by optical and scanning electron microscopy complemented with hardness allowed to evaluate the prior austenite grain size (PAGS) and homogeneity variations with heating rates, soaking time and temperature of austenitization. Their effect on the pearlitic transformation and the pearlite morphology, both at isothermal and continuous cooling, were also surveyed. While the heating rates do not seem to play an important role on the PAGS in the considered range, the results of the duration suggest a real effect on grain size, which are discussed based on diffusion process and by considering the time-temperature equivalences. The results collected in this work present guidelines for industrial practice and endorse the importance of parameters’ control in a heat treatment.