Introduction: The purpose of this study was to investigate whether the effects of renin.angiotensin system inhibitors (RASIs) after encircling ipsilateral pulmonary veins isolation (EIPVsI) for atrial fibrillation (AF) differed between patients with non-dilated and dilated left atria. Materials and methods: We retrospectively studied 292 consecutive patients (mean age=61 }11 years, 75% males) who underwent successful EIPVsI for paroxysmal or persistent AF. RASIs f effects were compared between the patients with a non-dilated left atrium of <40 mm (n=178) and dilated left atrium of .40 mm (n=114). Results: During a mean follow-up period of 18.9 }12.7 months, AF recurred in 38 (21.4%) and 45 (39.5%) patients with non-dilated and dilated left atria, respectively. A multivariate Cox proportional analysis revealed that treatment with RASIs (hazard ratio (HR) 0.30, 95% confidence interval (CI) =0.13.0.66, p=0.003), the duration of AF (HR 1.08/year, 95% CI=1.01.1.16, p=0.03), a history of hypertension (HR 2.86, 95% CI=188.8.131.52, p=0.02) and the left ventricular ejection fraction (HR 0.54/10%, 95% CI=0.34.0.87, p=0.01) were associated with AF recurrences in patients with a non-dilated left atrium. On the other hand, only the duration of AF (HR 1.11/year, 95% CI=1.01.1.21, p=0.03) was associated with AF recurrences in those with a dilated LA, and RASIs had no effect on AF recurrences (p=0.65). Conclusions: RASIs suppressed AF recurrences after EIPVsI only in patients with a non-dilated left atrium. © The Author(s) 2012.