Exercise-induced increase of the pulmonary arterial pressure may be an early sign of pulmonary arterial hypertension. It has been shown that patients with normal pulmonary arterial pressure at rest but elevated pulmonary arterial pressure during exercise have a decreased exercise-capacity and may have a worse prognosis compared to patients with normal pulmonary arterial pressure values at rest and during exercise. According to the currently used definition pulmonary hypertension can be diagnosed if the mean pulmonary arterial pressure is higher than 25mmHg at rest or 30mmHg during exercise. In this study patients with a risk for pulmonary arterial hypertension (connective tissue disease) and increased pulmonary arterial pressure values during exercise are receiving a therapy with a dual endothelin receptor antagonist - bosentan, a therapy established for pulmonary arterial hypertension. The therapy effect is than compared to the recorded changes before the introduction of this therapy.