Postoperative hypertension is commonly found in cardiac patients, and untreated hypertension patients may develop severe complications. This paper presents a gain-scheduling control system for postoperative blood pressure management. The system is based on a controller bank designed a priori using multiple-model control. A tuning method, which can effectively select a suitable control output, is then adopted. Each controller in the controller bank is a non-linear Proportional-Integral (PI) controller. The proportional and integral gains of the controller are updated using the error and the change of the plant, so that a wide range of parameter changes and non-linearities of the plant can also be handled. In simulation study, a non-linear pulsatile-flow model is used. This model can accurately describe the patient's plant. The simulation results show that the proposed gain-scheduling control system can effectively handle the changes in the patient's dynamics and provide satisfactory control performance.