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Long-acting calcium channel blockers are indicated in patients who have a "positive" response to the short-acting vasodilator challenge. In these patients, they have been shown to improve symptoms and prolong survival. If they fail to achieve significant improvement, an alternative therapy should be administered. They are contraindicated in patients who have no response or a "negative" response to the vasodilator challenge. In these patients, calcium channel blockers may worsen symptoms.