Apparatus and methods are described including an impeller that includes an impeller frame that comprises proximal and distal end portions and at least one helical elongate element that winds from the proximal end portion to the distal end portion. A film of material is coupled to the at least one helical elongate element, such that the helical elongate element with the film of material coupled thereto defines a blade of the impeller. The film of material is shaped to define a hollow central lumen therethrough. Other applications are also described.
