Apparatus, systems, and methods are provided for optimizing intracardiac filling pressures and cardiac output in patients with heart failure, conduction disease, and atrial fibrillation. The system is able to adjust and optimize intracardiac filling pressures and cardiac output by adjusting heart rate and the effective amount of total body blood volume. The device includes an adjustable member that may create a mean pressure differential in order to manifest an effective “mechanical diuresis” by sequestering extraneous blood volume to the high-capacitance of the venous vasculature. The system is therefore designed to reduce intracardiac filling pressures while maintaining or even increasing cardiac output.