1. A method of modeling a cardiac motion to generate a patient heart model, the method comprising: generating, by way of a processor, a 3-dimensional (3D) heart shape model; applying physical characteristics of a patient cardiac motion to the 3D heart shape model; obtaining, via a medical imaging device, cardiac ultrasound images according to a temporal change; obtaining a reference strain based on the cardiac ultrasound images; deriving a boundary condition by fusing the 3D heart shape model to which the physical characteristics are applied and the cardiac ultrasound images based on a position change of feature points over time in the cardiac ultrasound images; constructing the patient heart model and acquiring motion information by modeling the patient cardiac motion using the boundary condition; comparing the motion information and the reference strain; optimizing parameters reflecting the physical characteristics of the patient cardiac motion based on a result of the comparison; and diagnosing a cardiac disease based on the distribution of the motion information obtained using the optimized parameters.