A novel deformable model is proposed for efficient 3D visual tracking of beating heart. The model is parameterized by the 3D coordinates of four control points: the three vertices and the circumcenter of a triangular target region. Nonlinear deformation on heart surfaces is handled by cubic spline interpolation based on radial pixel distances from the circumcenter. With a pre-computable design matrix, the model can be represented efficiently by a simple matrix equation. An iterative algorithm is developed based on the efficient second-order minimization to compute model parameters at each frame. The proposed tracking method is validated on the stereo-endoscopic videos of phantom heart and in vivo heart that are recorded by the da Vinci ® surgical system.