An impeller includes a hub and a blade supported by the hub. The impeller has a stored configuration in which the blade is compressed so that its distal end moves towards the hub, and a deployed configuration in which the blade extends away from the hub. The impeller may be part of a pump for pumping fluids, such as blood, and may include a cannula having a proximal portion with a fixed diameter, and a distal portion with an expandable diameter. The impeller may reside in the expandable portion of the cannula. The cannula may have a compressed diameter which allows it to be inserted percutaneously into a patient. Once at a desired location, the expandable portion of the cannula may be expanded and the impeller expanded to the deployed configuration. A flexible drive shaft may extend through the cannula for rotationally driving the impeller within the patient.