Background: While several studies investigate the utility and clinical value of 3D printing in aiding diagnosis, medical education, preoperative planning, and intraoperative guidance of surgical interventions, there is a scarcity of literature regarding concrete applications of mixed reality in the cardiovascular domain due to its nascent stage of study and expansion. This study goes beyond a mere three-dimensional visualization of the cardiac district, aiming to visualize the intracardiac structures within the scope of preoperative planning for cardiac surgery. Methods: The segmentation of the heart was performed through an open-source and a professional software and by applying different procedures. Each anatomical component of the heart, including the aortic valve, was accurately segmented and a 3D model was built to represent the entire heart. Results: Beyond the three-dimensional visualization of the cardiac region, the intracardiac structures were also segmented. A mixed-reality app was implemented with the possibility of exploding the model, interacting with it, and freely sectioning it with a plane. Conclusions: The proposed segmentation methodology allows a segmentation of the valve and the intracardiac structures. Furthermore, the mixed-reality app has confirmed the potential of this technology in diagnostic and preoperative planning, although some limitations should still be overcome.