This case study describes the events of a patient who underwent an unintended invasive cardiac electrophysiology study. While reviewing the details of the case and the institution’s root cause analysis, the authors identify 17 distinct errors that culminated in the procedure taking place. The authors discuss the role of the individual versus the system, the existing culture contributing to the error, and strategies to avoid similar errors in the future. This article is part of a special collection entitled “Quality Grand Rounds,” a series of articles published in the Annals of Internal Medicine that explores a range of quality issues and medical errors.