1. A method for measuring left ventricle (LV) volume in a 3D cardiac volume, comprising: (a) receiving a 3D cardiac volume; (b) segmenting at least an LV endocardium and an LV epicardium in the 3D cardiac volume; (c) automatically determining an optimal threshold value based on intensities of voxels within the LV endocardium and voxels between the LV endocardium and the LV epicardium; (d) labeling each voxel within the LV endocardium as a blood pool voxel or a papillary muscle voxel based on the optimal threshold value; and (e) determining a volume of the LV based on the number of blood pool voxels.