BACKGROUND Atrial tachycardias (ATs) including atrial fibrillation are common arrhythmias occurring late after mitral valve (MV) surgery, and their management is challenging. OBJECTIVE The purpose of this study was to determine the electrophysiological mechanisms of ATs in patients with prior MV surgery and the long-term outcomes of catheter ablation. METHODS We studied 67 consecutive patients (mean age 59.4 10.6 years; 41 men [61%]) with prior MV surgery who presented with ATs postoperatively between 2007 and 2015. RESULTS AT was clinically documented before the electrophysiology study in 55 patients, whereas in the remaining 12 patients AT was inducible at the study. A total of 99 ATs (35 spontaneous and 64 inducible) were characterized. Overall, the right atrium (RA) was the chamber of origin in 56%. The underlying mechanism was macroreentry in 91 cases and included typical RA flutter (n = 37), mitral annular flutter (n = 21), incisional right AT (n = 16), roof-dependent reentry (n = 12), and local left atrial reentry (n = 5). Eight focal ATs were also documented: 6 from the left atrium and 2 from the RA. Left-sided ATs were more common in patients with prior Maze procedure (53%), and mitral annular flutter was twice as prevalent in this group (42% vs 210/0; P =.05). The ablation was acutely successful in 98.5%. Freedom from atrial arrhythmias was 62% at 12 months, with 42% requiring more than 1 procedure. CONCLUSION Macroreentry is the predominant AT mechanism in patients with prior MV surgery. Circuits are most often localized to the RA, with left-sided ATs more common in patients with prior Maze procedure. Repeat procedures are common and outcomes with 1 year complete AT control good.