"As Required" Oral Sildenafil in Raynaud's Phenomenon

Inclusion Criteria: * Active Raynaud's Phenomenon characterized by a clinical history of primary or secondary Raynaud's Phenomenon * At least 7 RP attacks per week on 5 or more days per week (assessed over the 2 weeks preceding inclusion) * Patients who have dated and signed the informed consent form * Contraception for women Exclusion Criteria: * Recently diagnosed RP (less than 2 months). * Uncontrolled hypertension, diabetes mellitus, angina * Haemodynamic instability * Nonarteritic ischemic optic neuropathy * Pulmonary hypertension * Subjects currently taking sildenafil, tadalafil or vardenafil * Subjects currently taking nitrates * Subjects currently taking strong CYP3A inhibitors * Pregnancy (or considering pregnancy in the next 4 months) * Breast feeding * Participation in another clinical trial