The effectiveness of clinical diagnosis and treatment of heart failure is a direct function of clinical signs that can be measured in a patient within cost and safety constraints. Large-scale mathematical modeling can be a key tool in revealing important, measurable clinical signs of heart failure, furthering medical understanding and development of treatment. In the first part of this study we have created two models of left heart failure--diastolic and systolic, using our human cardiovascular-respiratory system (H-CRS) model, and we present a comparison of the two types with emphasis on novel and differentiating clinical signs, such as tricuspid flow and septal motion. In the event of compromised left ventricular performance, mechanical left ventricular assist devices (LVAD) are often implanted to augment or completely replace the pumping action of the left ventricle (LV). One such type is the implantable rotary blood pump (iRBP). Several design issues related to the iRBP are difficult to study experimentally due to procedure complexity and limitations in animal models of heart failure . Therefore, modeling has become a key tool in iRBP development. In the second part of this study, we have introduced an iRBP model based on - in the systolic failing heart to study the interactions. We consider optimal motor settings for different levels of LV assistance, the effects of the iRBP on the right heart, septum, and pulmonary circulation. Our model results align with those reported in -. Improvement in cardiac output, pulmonary congestion, and heart work are seen with the iRBP. We observe lowered septal assistance to RV and LV ejection with increasing pump speeds, elevating right ventricular (RV) work, reducing LVET, and causing ventricular mechanical dyssynchrony in ejection. These results suggest right heart compromise via the septum's reduced role with the introduction of an iRBP. This work emphasizes the critical role of modeling in heart failure and treatment studies.