Clinical trials designed to evaluate the effect of drugs and devices on the symptoms and clinical status in chronic heart failure have frequently produced conflicting, inconclusive, or misleading results. These difficulties can be explained by the fact that previous studies have relied on efficacy measures that have inherent limitations and have been analyzed using statistical approaches that ignored episodes of clinical deterioration. Recognition of these pitfalls has led to the development of a new clinical composite score, which combines changes in the New York Heart Association class and the global assessment together with the information provided from the occurrence of major clinical events. Use of this score would have correctly distinguished active therapy from placebo in earlier trials and thus would have avoided some of their misleading conclusions. The new clinical composite score has been prospectively incorporated into the design of studies evaluating the efficacy of endothelin antagonists, cytokine antagonists, vasopressin antagonists, and cardiac resynchronization in the treatment of chronic heart failure. In the trials that have been completed to date, the clinical composite score has been more sensitive than conventional approaches in discerning the presence or absence of a true treatment effect.