IMPORTANCE Little is known regarding the durability of clinical practice guideline recommendations over time. OBJECTIVE To characterize variations in the durability of class I (“procedure/treatment should be performed/administered”) American College of Cardiology/American Heart Association (ACC/AHA) guideline recommendations. DESIGN, SETTING, AND PARTICIPANTS Textual analysis by 4 independent reviewers of 11 guidelines published between 1998 and 2007 and revised between 2006 and 2013. MAIN OUTCOMES AND MEASURES We 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. We classified recommendations replaced by less determinate or contrary recommendations as having been downgraded or reversed; we classified recommendations for which no corresponding item could be identified as having been omitted. We tested for differences in the durability of recommendations according to guideline topic and underlying level of evidence using bivariable hypothesis tests and conditional logistic regression. RESULTS Of 619 index recommendations, 495 (80.0%; 95%CI, 76.6%–83.1%) were retained in the subsequent guideline version, 57 (9.2%; 95%CI, 7.0%–11.8%) were downgraded or reversed, and 67 (10.8%; 95%CI, 8.4%–13.3%) were omitted. The percentage of recommendations retained varied across guidelines from 15.4%(95%CI, 1.9%–45.4%) to 94.1%(95%CI, 80.3%–99.3%; P < .001). Among recommendations with available information on level of evidence, 90.5%(95%CI, 83.2%–95.3%) of recommendations supported by multiple randomized studies were retained, vs 81.0% (95%CI, 74.8%–86.3%) of recommendations supported by 1 randomized trial or observational data and 73.7%(95% CI, 65.8%–80.5%) of recommendations supported by opinion (P = .001). After accounting for guideline-level factors, the probability of being downgraded, reversed, or omitted was greater for recommendations based on opinion (odds ratio, 3.14; 95%CI, 1.69–5.85; P < .001) or on 1 trial or observational data (odds ratio, 3.49; 95%CI, 1.45–8.41; P = .005) vs recommendations based on multiple trials. CONCLUSIONS AND RELEVANCE The durability of class I cardiology guideline recommendations for procedures and treatments promulgated by the ACC/AHA varied across individual guidelines and levels of evidence. Downgrades, reversals, and omissions were most common among recommendations not supported by multiple randomized studies.