<p>Left ventricular outflow tract obstruction (LVOTO) is a representative phenotype of obstructive hypertrophic cardiomyopathy (OHCM). Septal myectomy has been extensively demonstrated as an effective surgery for treating OHCM. However, it remains incompletely understood how the surgery would alter the mechanical and energetic states of the left ventricle (LV). In this study, microstructure-based finite element (FE) models were built for the LVs of two patients with OHCM to compute myocardial mechanics before and after septal myectomy. In addition, energy metrices spanning multiple scales were defined and calculated based on the results of FE analysis. The results showed that septal myectomy facilitated a significant improvement in the mechanical state of the LV, characterized mainly by the overall decreased while more homogeneously distributed myocardial tissue and cardiomyocyte stresses. Energetically, the total mechanical energies at the scales of the entire LV, myocardial tissue, and cardiomyocyte all decreased remarkably after septal myectomy. Moreover, the surgery induced a moderate increase in the efficiencies of mechanical energy conversion at the myocardial tissue and cardiomyocyte levels in the septal region. Although the mechanical and energetic parameters of the LV differed quantitatively between the two patients, they exhibited similar trends of change following septal myectomy. These results suggest that septal myectomy can improve the mechano-energetic state of the LV, and thereby may exert favorable influence on postoperative cardiac remodeling and adaptation. The proposed modeling method may offer a promising means for optimizing surgical planning or evaluating the therapeutic effects of septal myectomy for patients with OHCM.</p>