(EN) An implantable reservoir (3), (20), (30), (51) uses shape memory alloy as the driver to compress a reservoir housing (7), (22), (31, 32), (52, 53) thereby providing a constant pressure source fluid delivery device. The shape memory alloy may form either the reservoir itself by appropriate shaped sheets (1, 2) or it may form bands (21) around a flexible reservoir housing (22). The reservoir may also be formed of rigid clamped members (31), (32) or rigid pivoted members (52), (53) using shape memory alloy actuators (35), (62) to bias the rigid members together.