Three dimensional cultures in a microfabricated environment provide in vivo-like conditions to cells, and have used in a variety of applications in basic and clinical studies. Also, the analysis of the contractility of cardiomyocytes is important for understanding the mechanism of heart failure as well as the molecular alterations in diseased heart cells. This paper presents a realistic computational model, which considers the three dimensional fluid-structural interactions (FSI), to quantify the contractile force of cardiomyocytes on hybrid biopolymer microcantilevers. Prior to this study, only static modeling of the microscale cellular force has been reported. This study modeled the dynamics of cardiomyocytes on microcantilevers in a medium using the FSI. This realistic model was compared with static FEM analysis and the experimental results. Using harmonic response analysis in FSI modeling, the motion of a hybrid biopolymer microcantilever in the medium was identified as a second-order system and the influence of the dynamics of cardiomyocytes could be evaluated quantitatively.