A method of perfusing an ex-vivo organ or tissue, the method comprising: connecting a conduit to the organ or tissue, the conduit comprising a plurality of tubes, and a first end of each of at least two of said tubes being connected to the organ or tissue; applying a fluid motive force to a perfusion fluid in the two tubes to force the fluid through the two tubes into the organ or tissue to perfuse the organ or tissue; and allowing a flow balance to be established between the two tubes by the fluid motive force and backpressure generated by the organ or tissue being perfused, the method being further characterized by: disposing at least one valve on each of the two tubes; sensing with a detector the presence or absence of the at least one valve on each of the two tubes, the detector being configured to provide a signal indicative of the presence or absence of the at least valve on each of the two tubes to a controller; and if at least one valve is detected, then manually actuating the at least one valve to constrict at least one of the two tubes to alter the flow balance between the two tubes without altering the fluid motive force that is applied, wherein the controller is configured to control the perfusion of the ex-vivo organ or tissue according to a first mode of operation when the detector does not detect the presence of the at least one valve of the two tubes, the first mode of operation allowing the organ or tissue and a pump generating the fluid motive force to control flow rate and/or pressure of the perfusate fluid in the two tubes; and the controller is configured to control the perfusion of the ex-vivo organ or tissue according to a second, different mode of operation when the detector detects the presence of the at least one valve on each of the two tubes, the second mode of operation allowing a user to adjust one or more of the at least one valve on each of the two tubes to override the flow rate and/or the pressure produced by the organ or tissue and the pump. connecting a conduit to the organ or tissue, the conduit comprising a plurality of tubes, and a first end of each of at least two of said tubes being connected to the organ or tissue; applying a fluid motive force to a perfusion fluid in the two tubes to force the fluid through the two tubes into the organ or tissue to perfuse the organ or tissue; and allowing a flow balance to be established between the two tubes by the fluid motive force and backpressure generated by the organ or tissue being perfused, the method being further characterized by: disposing at least one valve on each of the two tubes; sensing with a detector the presence or absence of the at least one valve on each of the two tubes, the detector being configured to provide a signal indicative of the presence or absence of the at least valve on each of the two tubes to a controller; and if at least one valve is detected, then manually actuating the at least one valve to constrict at least one of the two tubes to alter the flow balance between the two tubes without altering the fluid motive force that is applied, wherein the controller is configured to control the perfusion of the ex-vivo organ or tissue according to a first mode of operation when the detector does not detect the presence of the at least one valve of the two tubes, the first mode of operation allowing the organ or tissue and a pump generating the fluid motive force to control flow rate and/or pressure of the perfusate fluid in the two tubes; and the controller is configured to control the perfusion of the ex-vivo organ or tissue according to a second, different mode of operation when the detector detects the presence of the at least one valve on each of the two tubes, the second mode of operation allowing a user to adjust one or more of the at least one valve on each of the two tubes to override the flow rate and/or the pressure produced by the organ or tissue and the pump. disposing at least one valve on each of the two tubes; sensing with a detector the presence or absence of the at least one valve on each of the two tubes, the detector being configured to provide a signal indicative of the presence or absence of the at least valve on each of the two tubes to a controller; and if at least one valve is detected, then manually actuating the at least one valve to constrict at least one of the two tubes to alter the flow balance between the two tubes without altering the fluid motive force that is applied, wherein the controller is configured to control the perfusion of the ex-vivo organ or tissue according to a first mode of operation when the detector does not detect the presence of the at least one valve of the two tubes, the first mode of operation allowing the organ or tissue and a pump generating the fluid motive force to control flow rate and/or pressure of the perfusate fluid in the two tubes; and the controller is configured to control the perfusion of the ex-vivo organ or tissue according to a second, different mode of operation when the detector detects the presence of the at least one valve on each of the two tubes, the second mode of operation allowing a user to adjust one or more of the at least one valve on each of the two tubes to override the flow rate and/or the pressure produced by the organ or tissue and the pump.