A total of 473 patients (mean age: 63 years; 73% male) underwent resection, 51% 2-stage, 18% 3-stage, 12% transhiatal, and 19% extended total gastrectomy. Ninety-six (20%) patients developed new-onset AF, in 18%, 27%, 29%, and 14% of 2-, 3-, transhiatal, and extended total gastrectomy cohorts, respectively (P=0.05). Age, diabetes, neoadjuvant therapy, and cardiac history predisposed (P<0.05) to AF, and AF was significantly (P<0.0001) associated with pneumonia, pleural effusions requiring drainage, and maximum postoperative C-reactive protein (CRP) (P<0.05) but not with anastomotic leak/conduit necrosis or mortality. Amiodarone was the primary treatment in 63% of cases, 1% underwent cardioversion, and 92% were in sinus rhythm on discharge. At a median follow-up of 40 months (7-109 months), the median survival was 40 months versus 53 months in the AF and non-AF cohorts, respectively (P=0.353) CONCLUSIONS: New-onset AF is common, linked to age, diabetes, cardiac disease, and neoadjuvant therapy. It is strongly associated with complications, principally respiratory sepsis, and systemic inflammation. For most, it resolves, with no impact on oncologic outcomes.