1. A computer implemented method of cardiac imaging, comprising the steps of: a. registering a pre-operative 3D volumetric dataset of a subject's coronary arteries with an ECG-gated angiogram sequence of a subject's heart; b. adjusting the registration of the pre-operative volumetric dataset with one of said ECG-gated angiograms using a respiratory motion reference model that optimizes 6 or fewer parameters that describe a rigid transform to estimate coronary pose parameters from similarity measures describing a distance between a set of 2D biplane fluoroscopic images and a coronary centerline in the pre-operative volumetric dataset; c. registering the pre-operative 3D volumetric dataset of the subject's coronary arteries with additional angiogram sequences of the subject's heart by using the reference model to restrict optimization of image alignments; and d. presenting registration results to respective cardiac imaging users, wherein said reference model of respiratory motion is a patient-specific model trained in a preparatory training phase, including acquiring an initial sequence of ECG-gated 2D biplane X-ray angiograms; registering a pre-operative 3D segmentation of the coronary arteries with the ECG-gated 2D biplane X-ray angiogram sequence; and estimating the pose of the vasculature in each sequence image by applying a feature-based rigid 2D/3D registration algorithm that best maps a pre-operative 3D centerline segmentation of the coronary arteries to the 2D biplane X-ray angiograms, wherein the coronary centerline is reconstructed from the pre-operative 3D segmentation, wherein for each breathing phase, an estimate for the cardiac pose represented by a rigid transform that forms a linear sub-manifold embedded in a six dimensional space of a rigid 3D transformation is obtained from a basis of a d-dimensional linear sub-manifold, d<=6, identified from a first d eigenvectors corresponding to a d largest eigenvalues of a covariance matrix of the linear sub-manifold.