<p>Heart failure with preserved ejection fraction (HFpEF) is a common yet highly complex form of heart failure (HF). A major challenge in obtaining market approval for medical devices targeting HFpEF treatment is the absence of highly controllable testing models. This work introduces an in-vitro, biomimetic, left-heart, atrioventricular simulator, with a closed-loop control system designed to model HFpEF disease progression. While at proof-of-concept stage, its unique capabilities show promise for higher-dimensional modeling than existing models. The simulator employs artificial muscle fibers which are highly controllable on their relaxation stroke. Its goal-oriented control system enables compliance modulation of the artificial myocardium during diastole. By setting hemodynamic targets, the myocardium dynamically responds, replicating the biomechanics of HFpEF progression. The model effectively recreates key hallmarks of HFpEF phenotypes, including impaired relaxation, pericardial restraint, and increased ventricular stiffness, capturing both hemodynamic and biomechanic aspects of the disease. Its capability is further validated, simulating mechanical circulatory support for HFpEF treatment. While more work is needed to demonstrate clinical application through control system development, actuation speed improvements, and further clinical validation, this work shows promise as a powerful tool for device development and pathophysiological studies, advancing our understanding and treatment of heart diseases.</p>