A 71-year-old woman presents to an ambulatory clinic with a chief complaint of dyspnea upon exertion. Over the past few weeks she has had a chronic cough and shortness of breath when walking more than two city blocks. She has a long history of hypertension that has been poorly controlled in recent years. On physical examination she has an elevated jugular venous pulse and rales are evident on lung examination. Cardiac enzyme tests are negative. What is the most appropriate next step in distinguishing systolic from diastolic heart failure