PH is an uncommon manifestation of SLE. The symptoms of PH develop within a few years after the onset of the multisystem disease. The most common presenting complaints of SLE patients with PH are dyspnea on exertion, chest pain, nonproductive cough, edema, and fatigue or weakness. The important physical findings are a loud second pulmonic heart sound and a right ventricular lift. The chest roentgenogram shows a cardiomegaly, a prominent pulmonary segment, and usually clear lung fields. Pulmonary function tests may show evidence of restrictive lung disease; however, the physiologic abnormalities are mild and out of proportion to the severity of the PH. The diagnosis of PH is established by cardiac catheterization showing elevated pulmonary artery pressure, normal capillary wedge pressure, and no evidence of intracardiac or extracardiac shunts. Pathologic examination of the lung demonstrates angiomatoid lesions involving muscular pulmonary arteries. There is a thickening of the media and subintima of the arterioles. Immunoglobulin and complement deposits are found in the walls of pulmonary arteries. Immunoglobulin eluted from the lung contains rheumatoid factor and antinuclear antibody including antibody to DNA activity. DNA antigen is also present in walls of blood vessels. These results suggest an immune complex deposition process as a mechanism in the pathogenesis of PH in SLE. The clinical course of PH in SLE is variable. Symptoms may be mild and the disease follows a stable and protracted course for several years. It can, however, develop a progressive course ending in death in a few years. The clinical response of SLE patients with PH to treatment with high doses of systemic corticosteroids is not consistent or predictable.