An apparatus for assisting the function of a heart disposed within a body. The apparatus can apply a compressive force and an expansive force to a portion of the outer wall of the heart. The apparatus can comprise a cup-shaped shell having an exterior wall, an interior wall, an apex, and an upper edge; a liner having an outer surface and an inner surface, an upper edge joined to the interior wall of the cup-shaped shell, and a lower edge joined to the interior wall of the cup-shaped shell, thereby forming a cavity between the outer surface thereof and the interior wall of the shell; and a drive fluid within the cavity. The drive fluid can apply a force on a portion of the outer wall of the heart.