The priority queueing discipline plays a crucial role in the Differentiated Services (DiffServ) architecture. Analytical modelling and performance evaluation of priority queueing systems have received significant research efforts in the telecommunication community. However, most existing studies have primarily focused on the analysis of such systems under either Short Range Dependent (SRD) or Long Range Dependent (LRD) traffic only. With the aim of investigating the impact of heterogeneous traffic on the design and performance of telecommunication networks, this paper presents an analytical model for priority queueing systems subject to heterogeneous LRD self-similar and SRD Poisson traffic. We extend the application of the generalized Schilder?s theorem to deal with heterogeneous traffic and further develop the analytical upper and lower bounds for the queue length distributions of individual traffic flows. Through extensive comparisons between analytical bounds and simulation results, we validate the effectiveness and accuracy of the developed model.