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Excised sheets of canine myocardium were subjected to cyclic loading and unloading in the predominant fibre and cross-fibre directions to determine passive mechanical properties. Myocardium under biaxial loading exhibits both non-linear elasticity and viscoelasticity with some strain-rate dependence in the position of the stress-strain relations, but very little rate dependence in the area enclosed by the loading and unloading portions of the stress-strain loops. Fibre and cross-fibre directions demonstrate anisotropic behaviour, with both the degree and direction of the anisotropy being dependent upon the region of the heart from which specimens are obtained. In the same specimen biaxial as compared with uniaxial loading yields different interpretations as to the material properties.
Demer et al. (Wed,) studied this question.