A 78-year-old woman presents to the emergency department with a one-year history of progressive dyspnea on exertion and fatigue. Her symptoms have acutely worsened over the past week, and she now becomes breathless walking from her bedroom to the kitchen. For the last two nights, she has woken up gasping for air and needs to sleep on three pillows. She also reports intermittent palpitations. Her past medical history is significant for hypertension and chronic kidney disease stage 3. She denies any history of rheumatic fever.