Inclusion Criteria:

• Male or female subjects between the ages of 18 years and 60 years will be selected for the study if they have a clinical diagnosis of Raynaud's phenomenon secondary to systemic sclerosis (scleroderma). Raynaud's phenomenon is defined as a history of cold sensitivity associated with colour changes of cyanosis or pallor, as well as a history of at least 4 attacks per week during two pre-trial period even with treatment with other vasodilators. The diagnosis of scleroderma is defined by the American College of Rheumatology (ACR) criteria or by the presence of at least 3 of the 5 features of the CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasias).

Exclusion Criteria:

Patients will be excluded if they have:

• Symptomatic orthostatic hypotension
• Evidence of current malignancy
• History of sympathectomy
• Upper extremity deep vein thrombosis or lymphedema within 3 months
• Recent surgical procedure requiring general anesthesia
• AMI, unstable angina, strokes and TIA within the past three months
• Smoking
• Use of any investigational drug within 30 days of the study sessions
• Use of medications that might interfere with tadalafil like nitrates and alpha adrenergic blockers that have vasoactive effects, and patients taking potent inhibitors of CYP3A4 such as ritonavir, ketoconazole, and itraconazole, erythromycin, itraconazole, and grapefruit juice
• Patients taking alcohol
• Patients with bleeding disorders
• Significant active peptic ulceration
• Current pregnancy
• Current breast-feeding