This is a reminder that in our zeal to help patients we can do more harm than good by uncritically applying clinical trial results to daily patient care. On a per-patient basis, RALES showed the largest absolute difference in survival for any large-scale clinical trial testing drug therapy in patients with chronic systolic heart failure. The publication of RALES was NOT associated with significant decreases in the rates of readmission for heart failure or death. How could increased use of a drug that performed so well in a clinical trial not translate to better results in the real world? Internal validity is the extent to which a clinical trial accurately proves that the tested treatment directly caused the observed results.