New emerging applications for wireless sensor networks as mission-critical and multimedia applications often have heterogeneous sensing capabilities and require that the network supports different types of QoS-constrained traffic at variable rates. Designing an efficient Medium Access Control protocol allowing these applications to work properly while coping with the limited resources of sensor networks is a challenging task. In this paper, we present AMPH, a new adaptive MAC protocol with QoS support for heterogeneous wireless sensor networks. AMPH provides high channel utilization with a hybrid and adpative behavior and integrates a new efficient prioritization scheme to provide QoS support and fair data delivery of heterogeneous traffic. The simulation results show the effectiveness of AMPH.