The geometries of sub-cellular structures in cardiac myocytes play a critical role in regulating the cells' functions. We present a chain of image and geometric processing approaches for constructing multi-scale and realistic models of 3D cardiac cells. Two types of imaging data are considered: one is the confocal light microscopy images of whole cells and the other is the electron microscopy images of individual calcium release units (CRUs). Images are pre-processed by anisotropic filtering and contrast enhancement techniques. Sub-cellular structures are extracted by automatic image analysis approaches including 3D image segmentation and skeletonization. High quality surface and volumetric meshes are generated for finite element simulation of excitation-contraction (E-C) coupling in cardiac myocytes.