A percutaneous heart valve prosthesis (1) has a valve body (2) with a passage (9) extending between the first and second ends (7, 8) of the valve body (2). The valve body (2) is collapsible about a longitudinal axis (10) of the passage (9) for delivery of the valve body (2) via a catheter (18). One or more flexible valve leaflets (3, 4) are secured to the valve body (2) and extend across the passage (9) for blocking bloodflow in one direction through the passage (9). An anchor device (5), which is also collapsible for delivery via catheter (18), is secured to the valve body (2) by way of an anchor line (6). A failed or failing mitral heart valve (101) is treated by percutaneously locating the valve body (2) in the mitral valve orifice (102) with the anchor device (5) located in the right atrium (107) and engaging the inter-atrial septum (103), such that the taught anchor line (6) acts to secure the valve body (2) within the mitral valve orifice (102).
