A 34-yr-old woman with mixed connective tissue disease (MCTD) who died of heart failure due to pulmonary hypertension (PH) is reported. She showed various symptoms and signs over the previous 8 yr, including lymphadenopathy, Raynaud's phenomenon, polyarthralgia, sclerodactylia, esophageal disturbance, PH, Sjögren's syndrome and renal tubular acidosis. Autopsy findings revealed severe intimal proliferation with marked luminal narrowing of the small arteries in the lung. Echocardiographic and mechanocardiographic methods were very useful for assessment of the degree of right ventricular dysfunction associated with PH on the early stage of MCTD.