A system (100) for segmenting a coronary artery vessel tree (182) of a patient heart in a three dimensional (3D) cardiac image (120) includes a coronary volume definition unit (150) and a coronary artery segmentation unit (180). The coronary volume definition unit (150) sets a spatial boundary (210, 220) from internal and external surfaces of heart tissues in the 3D cardiac image based on a fitted heart model (200). The coronary artery segmentation unit (180) segments the coronary artery vessel tree (182) in the 3D cardiac image using a segmentation algorithm with a search space limited by the spatial boundary set from the internal and external surfaces of the heart tissues.