A 38-year-old woman from rural Maharashtra presents with progressive exertional dyspnea, orthopnea, and hemoptysis for 6 months. She has a history of recurrent sore throat in childhood. On examination, she has malar flush, loud S1, and a mid-diastolic rumbling murmur at the apex. Echocardiography confirms mitral stenosis with a valve area of 1.2 cm². The gross pathology specimen shows the atrial view of the mitral valve with the structure marked **A** — a narrowed orifice with characteristic appearance. Which of the following best describes the pathophysiological consequence of the structural deformity marked **A**?