Understanding and predicting the mechanical behavior of myocardium under healthy and pathophysiological conditions are vital to developing novel cardiac therapies and promoting personalized interventions. Within the past 30 years, various constitutive models have been proposed for the passive mechanical behavior of myocardium. These models cover a broad range of mathematical forms, microstructural observations, and specific test conditions to which they are fitted. We present a critical review of these models, covering both phenomenological and structural approaches, and their relations to the underlying structure and function of myocardium. We further explore the experimental and numerical techniques used to identify the model parameters. Next, we provide a brief overview of continuum-level electromechanical models of myocardium, with a focus on the methods used to integrate the active and passive components of myocardial behavior. We conclude by pointing to future directions in the areas of optimal form as well as new approaches for constitutive modeling of myocardium.

Significance: Percutaneous valve replacement procedures enable the deployment of bioprosthetic heart valves through a catheter, which offers a minimally invasive option to treat valvular heart disease. Although these bioprostheses typically employ thinner leaflet tissues to accommodate the collapsed valve dimensions, the impact of using such tissues remains poorly understood. This study used high-fidelity computational methods to model realistic aortic valve implants and analyze the behavior of thinner tissues in the valvular system. The results from this investigation provide essential knowledge about a previously understudied phenomenon and indicate that thinner, more flexible biological tissues induce significant leaflet flutter during the cardiac cycle. This observed response introduces blood flow disturbances and leaflet irregularities that can lead to cardiovascular dysfunction and reduced valve durability.