In LTE-Advanced networks, the steady demand for higher data rates by users is met through several techniques. One of the most promising solutions is CoMP (Coordinated MultiPoint), which allows the involvement of multiple eNB in the transmission and reception process with a marked increase in throughput for users at the edge of cells. While downlink CoMP has been the focus of many works in the literature, in this paper we examine Uplink CoMP with Coordinated Scheduling in Heterogeneous Networks running LTE-A. We investigate its system-level performance through simulation in various realistic scenarios with frequency-selective Rayleigh fading. Specifically, we are interested in comparing the performance of Uplink CoMP with different cell types as well as different user participation to CoMP transmissions. Our simulation results confirm that edge users benefit from Uplink CoMP, although the overall throughput decreases. In order to mitigate the latter effect, we introduce two new parameters, called CoMP margin and CoMP Pool Percentage (CPP), and provide guidelines for their effective use.