As a well-known property of the heart, many studies has reported that the left ventricular end-systolic pressurevolume relationship (ESPVR) is linear. However, the reason of the linearity is poorly understood. This article presents a multiscale circulation model to be a tool for theoretical analyses on the mechanism of the linearity of ESPVR. The model is composed of three sub-models; a detailed closed-loop lumped-parameter model for cardiovascular system, geometric left ventricle model, a comprehensive ventricular myocyte model. Although the present model integrates nonlinear sub-models, the model can successfully reproduce highly linear ESPVR without any arbitrary modifications.