1. A method for fusion of a model of a target cardiac structure extracted from a first medical image of a patient acquired using a first imaging modality with a second medical image of the patient acquired using a second imaging modality, comprising: segmenting a first pericardium model in the first medical image; segmenting a second pericardium model in the second medical image; estimating a deformation field between the first pericardium model and the second pericardium model; and fusing the model of the target cardiac structure extracted from the first medical image with the second medical image based on the estimated deformation field between the first pericardium model and the second pericardium model, wherein the target cardiac structure is a cardiac structure other than the pericardium and the pericardium is used as anchor structure to fuse the target cardiac structure to the second medical image.