Elastomechanical modeling constitutes an essential step for realistic computer simulations of the cardiac system. The deformation of tissue effects e.g. cellular electrophysiology, which is commonly neglected in electrophysiological simulations due to the lack of efficient mechanical models. This work focuses on extending a mechanical deformation model by including blood pressure as endocardial boundary condition. Four phases are distinguished in a normal heart cycle: isovolumic contraction, isotonic contraction, isometric relaxation, and isotonic relaxation. The first three phases were modeled. The methods modeling intraventricular pressure corresponding to contraction phases are illustrated, applied, and discussed. Simulation results show that the mechanical model is capable of incorporating a pressure load leading to a more realistic contraction behavior. Furthermore, the ejection curve resembles in closer detail measured data