This paper investigates the two-hop communication between a source and a destination with the aid of an intermediate half-duplex relay node. There is no direct link between the source and the destination. Both the source and intermediate relay node are assumed to operate under statistical quality of service (QoS) constraints imposed as limitations on the buffer overflow probabilities. It is further assumed that the nodes send the information at fixed power levels and have perfect channel side information. In this scenario, the maximum constant arrival rates that can be supported by this two-hop link are characterized by finding the effective capacity. Through this analysis, the impact upon the throughput of using half-duplex relays and having buffer constraints at the source and relay nodes is identified.