Congenital heart diseases (CHD) are the leading cause of death related to birth defect. Among all the possible cardiac malformation and changes in the heart structure, ventricular septal defects (VSDs) are the most common, accounting for 20 – 25 % of all CHDs [1]. In this work, a computational framework is presented for the investigation of cardiac dynamics in the presence of ventricular septal defects, with particular emphasis on its electromechanical behavior. The numerical method is based on the coupling between the monodomain model and a novel active strain approach tailored for the interaction potentials model for the myocardium mechanics [2]. The active strain is evaluated from the calcium concentration signal traveling along the fiber; deformation in sheet and normal directions are evaluated either assuming orthotropic or transversally isotropic behavior of the myocardium [3]. Patient-specific ventricular geometries are obtained from an open-access cardiac MRI dataset which provides whole-heart segmentations of patients affected by several CHDs [4]. Numerical simulations are performed over a full cardiac cycle to track in time the evolution of the defect’s effective area, perimeter and shape in order to evaluate the effect of the model used to relate myocardium material properties with the fiber direction. This electromechanical study also provides useful indications for the optimal selection of computational grids when performing fluid structure interaction simulations helping to avoid under-resolution of the ventricular defect during the cardiac cycle. REFERENCES [1] Center for Disease Control and Prevention (CDC). Trends in infant mortality attribute to birth defects – United States, 1980-1995. Morbidity and Mortality Weekly Report, 47, 773-778, 1998. [2] Fedosov, Dmitry A., Bruce Caswell, and George Em Karniadakis, Systematic coarse-graining of spectrin-level red blood cell models, Computer Methods in Applied Mechanics and Engineering, 199.29-32 (2010): 1937-1948. [3] Propp A, Gizzi A, Levrero-Florencio F, Ruiz-Baier R. An orthotropic electro-viscoelastic model for the heart with stress-assisted diffusion. Biomechanics and Modeling in Mechanobiology. 2020 Apr;19(2):633-59. [4] Danielle F. Pace et. al., HVSMR-2.0: A 3D cardiovascular MR dataset for whole-heart segmentation in congenital heart disease, Sci Data, 11, 721 (2024).