The importance of realistic cardiac MR simulation has been realized over the past decade. For this application, XCAT phantom provides realistic highly detailed whole body anatomical models including the heart and respiratory motion. Although the current XCAT heart model is complete in terms of substructures, the trabeculae structure of the endocardium, which is geometrically complex, is lacking. Based on a high-resolution ex-vivo cardiac image data, we modeled and incorporated the irregularity of the trabeculae into the existing XCAT model. We demonstrated that greater realism in cardiac MRI simulation can be achieved by including the trabeculae anatomy into the heart.