Weng W, Wiefels C, Chakrabarti S, et al. - This substudy of the CHASM‐CS (Cardiac Sarcoidosis Multicenter Prospective Cohort Study) was performed to determine the frequency of atrial arrhythmias (AAs) as the presenting feature of previously undiagnosed cardiac sarcoidosis (CS). Additionally, AA incidence, burden, predictors, and response to immunosuppression were ascertained by utilizing prospective follow‐up data from implanted devices. The following inclusion criteria were applied: presentation with clinically manifest cardiac sarcoidosis, treatment‐naive status, and implanted with a device that reported precise AA burden. These inclusion criteria were satisfied by 33 patients (aged 56.1±7.7 years, 45.5% women). According to findings, clinically manifest cardiac sarcoidosis was rarely presented by episodes of AAs. The occurrence of AAs was found in a minority of patients at follow‐up; very low burden was noted in most patients. Clinically significant AA burden was found in only 2 patients, and both showed a reduction after CS was treated.