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.