Question

A 24-year-old primigravida at 28 weeks gestation presents to the obstetrical triage unit complaining of worsening shortness of breath and a cough that is occasionally productive of blood-streaked sputum. She immigrated to the United States two years ago and has had limited prior medical care. The patient notes that her breathing is significantly worse when she attempts to lie flat in bed. Temperature is $37.1^\circ\text{C}$ ($98.8^\circ\text{F}$), blood pressure is $108/68\text{ mmHg}$, pulse is $118/\text{min}$ and regular, and respirations are $26/\text{min}$. Pulse oximetry ($SpO_2$) is $92\%$ on room air. Physical examination shows jugular venous distention. Lung auscultation reveals bilateral crackles in the lower lung fields. Cardiac auscultation in the left lateral decubitus position demonstrates a prominent first heart sound ($S_1$) and a low-pitched, mid-diastolic rumble at the apex. Which of the following is the most appropriate next step in patient care?