A delivery device for deploying a self-expanding implant within a body cavity, the device comprising: at least one retention formation for holding the implant against axial or circumferential movement; an elongate longitudinally-extending outer element (48, 206), radially outboard of the or each retention formation; an imaging head (90, 202) disposed on a longitudinal axis that extends on a radially-inboard side of the or each retention formation; and a handle connected to a proximal end of the outer element (48, 206), the or each retention formation being fixed axially relative to the handle, and the outer element (48, 206) and the imaging head (90, 202) being movable axially relative to the handle; wherein the outer element (48, 206) is movable bidirectionally in longitudinal directions relative to the handle between: a storage position in which the outer element (48, 206) surrounds the implant and holds the implant engaged with the or each retention formation; and a partial-deployment position in which the outer element (48, 206) uncovers a distal portion of the implant while surrounding a proximal portion of the implant to continue holding the implant engaged with the or each retention formation; and the imaging head (90, 202) is retractable in a proximal direction relative to the handle from: an advanced position when the outer element (48, 206) is in the storage position; to a retracted position when the outer element (48, 206) is in the partial-deployment position. at least one retention formation for holding the implant against axial or circumferential movement; an elongate longitudinally-extending outer element (48, 206), radially outboard of the or each retention formation; an imaging head (90, 202) disposed on a longitudinal axis that extends on a radially-inboard side of the or each retention formation; and a handle connected to a proximal end of the outer element (48, 206), the or each retention formation being fixed axially relative to the handle, and the outer element (48, 206) and the imaging head (90, 202) being movable axially relative to the handle; wherein the outer element (48, 206) is movable bidirectionally in longitudinal directions relative to the handle between: a storage position in which the outer element (48, 206) surrounds the implant and holds the implant engaged with the or each retention formation; and a partial-deployment position in which the outer element (48, 206) uncovers a distal portion of the implant while surrounding a proximal portion of the implant to continue holding the implant engaged with the or each retention formation; a storage position in which the outer element (48, 206) surrounds the implant and holds the implant engaged with the or each retention formation; and a partial-deployment position in which the outer element (48, 206) uncovers a distal portion of the implant while surrounding a proximal portion of the implant to continue holding the implant engaged with the or each retention formation; and the imaging head (90, 202) is retractable in a proximal direction relative to the handle from: an advanced position when the outer element (48, 206) is in the storage position; to a retracted position when the outer element (48, 206) is in the partial-deployment position. an advanced position when the outer element (48, 206) is in the storage position; to a retracted position when the outer element (48, 206) is in the partial-deployment position.