The current technologies have made it possible to execute parallel applications across heterogeneous platforms. However, the performance models available do not provide adequate methods to calculate, compare and predict the applications performance on these platforms. In this paper, we discuss an enhanced performance evaluation model for parallel applications on heterogeneous systems. In our analysis, we include machines of different architectures, specifications and operating environments. We also discuss the enabling technologies that facilitate such heterogeneous applications. The model is then validated through experimental measurements using an agent-based parallel Java system, which facilitates simultaneous utilization of heterogeneous systems for parallel applications. The model provides good evaluation metrics that allow developers to assess and compare the parallel heterogeneous applications performances.