The pump which is for implantation into a human heart has a flow path through a housing (1 ) a rotatable pump member (21 ) within the housing for causing fluid to flow along the flow path the pump member being rotatably coupled to the housing about an upstream bearing (32) and a downstream bearing (33). The downstream bearing comprises a bearing member (34) on the pump member and a complementary bearing formation (35) on the housing The pump has a mechanical adjuster (42) for fine adjustment of the position of the bearing formation (35) along an axis (A) of the pump member； the mecahnical adjuster being preferably one or more screws (42) for adjustable movement of a boss (40) along the axis (A) the adjustable movement being permitted by flexure of a plate member (41) integral with the boss.
