A 27-year-old primigravida at 12 weeks gestation presents to the obstetric clinic with progressive dyspnea on exertion over the past 6 weeks. She reports that she can now only walk up one flight of stairs before needing to rest. She denies chest pain, orthopnea, or paroxysmal nocturnal dyspnea. Heart rate is 92 bpm, blood pressure 118/76 mmHg, and respiratory rate 18/min. Cardiac examination reveals a grade 3/6 low-pitched, rumbling diastolic murmur best heard at the apex with the patient in the left lateral decubitus position. There is an opening snap audible shortly after S2. Lung examination is clear bilaterally. Chest X-ray shows mild pulmonary congestion without cardiomegaly. Which of the following physiologic changes in pregnancy is the primary mechanism for this patient's clinical deterioration?

1. A)Decreased systemic vascular resistance leading to right-to-left shunting
2. B)Increased left ventricular afterload due to aortic stiffening
3. C)Expansion of intravascular volume with increased cardiac output demandsGABARITO
4. D)Decreased plasma oncotic pressure resulting in pulmonary edema
5. E)Increased heart rate causing prolonged diastolic filling time