Many patients who are enrolled in controlled clinical trials of new drugs for the treatment of heart failure show favorable hemodynamic and clinical responses to placebo therapy. This "placebo effect" results from both the creation of a supportive therapeutic environment and the spontaneous improvement that is commonly seen when measurements of symptoms and cardiac function are repeated frequently over long intervals of time. Three months of treatment with a placebo produces a reduction in symptoms in 25% to 35% of patients, an increase in cardiac output and a decrease in pulmonary wedge pressure, and an increase in exercise tolerance of up to 90 to 120 seconds. Physicians commonly seek to maximize the "placebo effect," since the goal of treatment in the clinical setting is to improve the quality of the patient's life. On the other hand, clinical investigators seek to minimize the "placebo effect," since the goal of a research study is to test the hypothesis that the new drug is superior to a placebo.