ABSTRACT
From the perspective of engineering mechanics, the ventricles are three-dimensional thick-walled pressure vessels with substantial variations in wall thickness and principal curvatures both regionally and temporally through the cardiac cycle. The cardiac extracellular matrix primarily consists of the fibrillar collagens, type I and III, synthesized by the cardiac fibroblasts, the most abundant cell type in the heart. Collagen is the major structural protein in connective tissues, but only comprises 2-5% of the myocardium by weight, compared with the myocytes, which make up 90%. Most biomechanics studies of passive myocardial properties have been conducted in isolated, arrested whole-heart or tissue preparations. Hence, the classical linear theory of elasticity is quite inappropriate for resting myocardial mechanics. The hysteresis of the tissue is consistent with a viscoelastic response, which is undoubtedly related to the substantial water content of the myocardium.
