An 80-year-old woman comes to the urgent care clinic with dyspnoea on exertion. On physical examination, her blood pressure is 100/70, and her pulse is 75. She has no pulsus paradoxus. Her jugular veins are distended, and she has distant heart sounds. In addition, she has extra third and fourth heart sounds. Her liver is enlarged, and she has pedal oedema. She has occasional premature ventricular contractions on her electrocardiogram. A chest x-ray reveals clear lung fields with a dil...