A 35 year old female with a history of HIV presents with increasing dyspnea on exertion. Her temperature is 37.0, blood pressure 120/80, heart rate 110, respirations 20, and oxygen saturation 95% on room air. Physical examination reveals normal breath sounds, elevated jugular venous pressure with large V waves, a III/VI holosystolic murmur at the right lower sternal border which becomes louder with inspiration, a pulsatile liver, and 2+ lower extremity edema. Her chest x-ray is below. Which of the following is most likely contributing to her dyspnea?