The heat transfer process that takes place in the interface between the working fluid and the cylinder walls is one of the most relevant effects regarding reciprocating compressor performance. The fast transients and the limitations in terms of space to install probes imply severe restrictions to the experimental analysis of this phenomenon. On the other hand, it is always desired to develop effective numerical simulation to describe such a phenomenon without computational time penalties. This paper presents a numerical analysis of the instantaneous heat transfer between gas and cylinder in reciprocating compressors under actual operating conditions, with an assessment of the influence of suction and discharge processes. The analysis was done on actual ۳D geometry including the movement of valves and remeshing through the simulation to guarantee mesh quality. Distribution of transferred heat among the main typical surfaces inside the cylinder is described in detail. Additionally, predictions for heat transfer are compared with experimental result. It is found that heat transfer is strongly affected by suction and discharge processes and good agreement was observed between prediction and experimental data for temperature