Background. The effect of metabolic syndrome (MetS), defined as insulin resistance along with two or more of: obesity, atherogenic dyslipidaemia and elevated blood pressure, on post-operative complications after isolated heart valve intervention remains controversial. We hypothesized that MetS may negatively influence the post-operative course in these patients. Methods. Patients from 10 cardiac units who underwent isolated valve intervention (mitral ± tricuspid repair/replacement (MVS) or aortic valve replacement (SAVR), or transcatheter aortic valve replacement (TAVR) were included. MetS was defined according to the WHO criteria. Primary outcome was in-hospital mortality and overall post-operative length of stay. Relevant post-operative complications were also recorded. Results. From 2010 to 2019, 17283 patients underwent valve intervention. The MVS, SVAR and TAVR accounted for the 39.4%, 48.2% and 12.3% respectively of the whole. MetS compared to no-MetS was associated to higher mortality in the MVS group (6.5% vs. 2%, p<0.001), but not in the SAVR and TAVR group. In both surgical cohorts, MetS was associated with increased complications including red blood cells transfusion, renal failure, mechanical ventilation time, intensive care and overall post-operative length of stay (11 (9) vs. 10 (6), p<0.001 and 10 (6) vs. 10 (5) days, p=0.002, MVS and SAVR)). No differences were found in the TAVR cohort, with similar mortality and complications. Conclusion. MetS was associated to more post-operative complications, with higher mortality in the MVS group. In the TAVR cohort, post-operative complications and mortality rate did not differ between patients with and without MetS, however length of stay was longer in the MetS group.