This paper describes a 61-year-old woman who presented with mixed connective tissue disease, which was complicated by the development of pulmonary arterial hypertension (PAH). Her condition worsened rapidly, with development of haemopthysis, tachypnoe and cardiac arrest. Doppler echocardiography showed a high systolic pulmonary arterial pressure (98 mmHg), confirmed by the right heart catheterization. Vasculopathy of the pulmonary artery vessels was detected following open lung biopsy. No pulmonary embolism was found. Because of suspicion of flare of her underlying disease, which leads to PAH, immunosuppressive treatment was started with high doses of corticosteroid and cyclophosphamide, in combination with the prostacyclin analogue, Iloprost, and low molecular weight heparin. The therapy resulted in slow recovery over 6 weeks, with control echocardiography showing normalization of the high pulmonary pressure, and the patient being capable of returning to everyday activities.