A valve holder for holding and implanting a prosthetic heart valve comprising a frame and a plurality of flexible leaflets, the valve holder comprising: a body for holding the prosthetic heart valve, the body having a proximal end, a distal end, and a central axis extending between the proximal and distal ends; an insert positioned in a bore of the body and being connectable to a handle; a piston attached to the body and to the insert and being configured to be positioned at least partially in the body, wherein when the prosthetic heart valve is held by the body, the piston is configured to translate relative to the body along the central axis to adjust the prosthetic heart valve to a delivery position; a suture mount for routing sutures connecting the valve holder to the prosthetic heart valve; and a shaft for connecting the piston to the suture mount; wherein the piston is configured to move axially relative to the body from a first configuration to a second configuration, such that the piston is further from the proximal end of the body in the second configuration than in the first configuration, wherein the body comprises a hub and a plurality of arms, the arms being flexible to allow the body to deform for insertion into a small surgical opening, and wherein the flexible arms of the body are configured to deform inwards in a direction towards the hub such that a maximum width of the body decreases when the arms are deformed, wherein the insert is between the piston and the body, and configured to threadably engage the handle to adjust the piston from the first configuration to the second configuration, and wherein in the second configuration the piston and the suture mount are located to place tension in the sutures to radially urge commissure posts of the prosthetic heart valve inwards. a body for holding the prosthetic heart valve, the body having a proximal end, a distal end, and a central axis extending between the proximal and distal ends; an insert positioned in a bore of the body and being connectable to a handle; a piston attached to the body and to the insert and being configured to be positioned at least partially in the body, wherein when the prosthetic heart valve is held by the body, the piston is configured to translate relative to the body along the central axis to adjust the prosthetic heart valve to a delivery position; a suture mount for routing sutures connecting the valve holder to the prosthetic heart valve; and a shaft for connecting the piston to the suture mount; wherein the piston is configured to move axially relative to the body from a first configuration to a second configuration, such that the piston is further from the proximal end of the body in the second configuration than in the first configuration, wherein the body comprises a hub and a plurality of arms, the arms being flexible to allow the body to deform for insertion into a small surgical opening, and wherein the flexible arms of the body are configured to deform inwards in a direction towards the hub such that a maximum width of the body decreases when the arms are deformed, wherein the insert is between the piston and the body, and configured to threadably engage the handle to adjust the piston from the first configuration to the second configuration, and wherein in the second configuration the piston and the suture mount are located to place tension in the sutures to radially urge commissure posts of the prosthetic heart valve inwards.