1. A method of modeling a cardiac motion, the method comprising: generating, by way of a processor, a 3-dimensional (3D) heart shape model; applying physical characteristics of a cardiac motion to the 3D heart shape model; obtaining a plurality of cardiac ultrasound images according to a temporal change to obtain a dynamic image; deriving a boundary condition by fusing the 3D heart shape model to which the physical characteristics are applied and the plurality of cardiac ultrasound images; and modeling the cardiac motion using the boundary condition.