To characterize variations in class I American College of Cardiology/American Heart Association (ACC/AHA) guideline recommendations (“procedure/treatment should be performed/administered”), Neuman and colleagues reviewed 11 guidelines published between 1998 and 2007 and revised between 2006 and 2013. The authors abstracted all class I recommendations from the first of the 2 most recent versions of each guideline and identified corresponding recommendations in the subsequent version. Among the authors’ findings was that of 619 index recommendations, 495 were retained in the subsequent guideline version, 57 were downgraded or reversed, and 67 were omitted. Durability of the recommendations varied across individual guidelines and levels of evidence. In an Editorial, Shekelle discusses updating practice guidelines and communicating changes to relevant stakeholders.