Atrial fibrillation is an independent predictor of mortality in patients with HF and is associated with other markers of worse prognosis, such as history of hypertension, advanced age, higher New York Heart Association functional classification, and lower ejection fraction (11). A major therapeutic tenet is to control heart rate adequately in these patients, with many clinicians ascribing a lower heart rate to therapeutic efficacy. On the surface then, Castagno et al. (6) report the most intriguing and paradoxical finding in this study—the lack of association of resting heart rate and cardiovascular outcomes in the 15% of patients in this study with AF. The authors themselves look closely at their data and quite rightly suggest several reasons why this finding is likely correct. First, the statistical interaction (p < 0.001) is very indicative of a very strong interaction. Second, the authors' own analysis suggests that patients with AF really are different. Patients in sinus rhythm who were in the highest tertile of heart rate had lower ejection fraction and higher New York Heart Association functional class and were more likely to be diabetic than those in the lower tertiles. Among patients with AF, this was not seen. Additionally, the authors point out that other smaller cohorts have suggested there is no heart rate–outcome relationship when AF is present. In contrast, it must be pointed out that heart rate was determined by either auscultation or palpation and might thus have been inaccurate in those with AF (the so called “pulse deficit”) and so affected the analysis. It would be quite helpful, for purposes of verification, to review the heart rate in patients with AF by both electrocardiogram and physical exam to determine whether there is likely an issue with pulse deficit. The population of patients with implanted cardiac devices could be an important source of information. The question of heart rate and outcomes for patients in AF could be further evaluated—in fact expanded upon—with potential for analysis of peak heart rate, temporal trends, and other factors that might instead predict outcomes for this subgroup.