Cardiac electromechanical models can significantly advance diagnosis, prognosis, and therapy planning. Despite their importance in evaluating myocardial function, key mechanical parameters such as myocardial stiffness (MS) are still missing in clinical practice. While ultrafast ultrasound imaging (UUI) provides reliable and reproducible data, its use in parameter estimation is still restricted, limiting the potential for comprehensive modeling. Integrating UUI data with reduced-order 0D models addresses these limitations by enabling more robust parameter estimation and improved data interpretation. The approach also significantly reduces computational costs compared to 3D simulations. This work presents a closed-loop 0D model calibrated using UUI-based shear wave elastography (SWE), a noninvasive technique providing detailed MS profiles across the cardiac cycle. By integrating MS, the model accounts for both active and passive contributions to myocardial function, with a primary focus on the active component. Modeled using the Bestel-Clement-Sorine (BCS) framework, it has been optimized with the Covariance Matrix Adaptation Evolution Strategy (CMA-ES) algorithm and calibrated to healthy subject data. The aim is to develop a subject-specific tool for clinical studies supporting parameter calibration and integration into 3D simulations, while extending its application to pathological cases.