Valvular Heart Disease USMLE Step 1 Practice Question

A 29-year-old woman with a 3-year history of systemic lupus erythematosus presents to the emergency department with acute-onset dyspnea, orthopnea, and hemoptysis. She reports chest discomfort with exertion over the past week. Vital signs: BP 98/62 mmHg, HR 118/min, RR 24/min, SpO2 86% on room air. On cardiac auscultation, a holosystolic murmur is heard at the apex. Chest X-ray shows pulmonary edema with cardiomegaly. Transthoracic echocardiography demonstrates severe mitral regurgitation secondary to papillary muscle rupture, with a dilated left atrium, ejection fraction of 35%, and elevated pulmonary artery systolic pressure of 58 mmHg. Which of the following cardiac chambers experiences the most severe hemodynamic consequence from this valve pathology?