Patients who respond to shoacting vasodilators at the time of cardiac catheterization (a fall in mean pulmonary aerial pressure >=10 mmHg and a final mean pressure <40 mmHg) should be treated with calcium channel blockers. Typically, these patients require high doses (e.g., nifedipine, 240 mg/d, or amlodipine, 20 mg/d). Patients may have dramatic reductions in pulmonary aery pressure and pulmonary vascular resistance associated with improved symptoms, regressionof RV hyperophy, and improved survival now documented to exceed 20 years. However, <20% of patients respond to calcium channel blockers in the long term. These drugs are not effective in patients who are not vasoreactive. ref:Harrison&;s principles of internal medicine,ed 18,pg no 2079