Mitral Stenosis — Fish-Mouth Valve

A 35-year-old woman from rural India presents with progressive exertional dyspnea and orthopnea for 2 years. She has a history of acute rheumatic fever at age 15. On examination, she has an irregular pulse, a loud S1, and a low-pitched diastolic rumble at the apex. Echocardiography confirms mitral stenosis with a valve area of 1.2 cm². The pathological specimen shows that the structure marked **C** (thickened chordae tendineae) is shortened, fused, and restricts leaflet motion. Which of the following best explains the hemodynamic consequence of this pathological change?