Computational modeling of ventricular electromechanics is considered to be among the most promising approaches to gain novel insight into cardiac function in health and disease. Such models allow to integrate the wealth of available experimental data into a mechanistic framework which allows to study complex cause-effect relationships across several scales of biological organization ranging from subcellular processes such as cellular force genera-tion up to the organ scale. However, due to the enormous challenges involved in constructing such models, the number of available multiscale models is very limited. Their implementation resorts to very crude approximations which ignores many aspects of known biophysical details and/or uses extremely coarse spatio-temporal discretizations to reduce computational complexity. In this study we focus on a subset of the parametrization and validation issues in models of cardiac electromechanics. An experimental setup for measuring passive stress-strain relationships as well as isometric force transients in thin preparations of ventricular trabeculae or papillary muscles was developed along with a matching computer model to parametrize and validate passive and active mechanical model responses at the tissue scale.