Background: Cardiac surgery performed in patients with low body weight is a challenge for surgeons. Currently, such outcomes are mainly reported from European or North American centers. In this study, we review our cardiac surgery experience with neonates and infants weighing <2,500g. Methods and Results: We included patients with a body weight <2,500g who received cardiac surgery between January 2008 and December 2012. The survival outcome was compared to that of patients with large body weight, and then the Risk Adjusted Classification for Congenital Heart Surgery (RACHS-1) categorization was used for operative risk stratification. In the 1,245 index operations, 53 patients (4.3%) were <2,500g. The mean body weight was 2,232g (range 1,320–2,500g). The hospital mortality rate was 20.7% (11/53). Most (85%) of the procedures were in RACHS-1 category ≥3. The risk ratio was significantly higher in RACHS-1 category 3 (relative risk [RR]:6.2; 95% confidence interval [CI]:1.6–23.9) and 4 (RR:4.6; 95% CI:1.4–15.0), respectively, while it was not significantly different in category 2 (RR:1.02; 95% CI:1.01–1.02) and category 6 (RR:2.9; 95% CI:0.36–13.3). Conclusions: Cardiac surgery performed on infants with low body weight is generally a complex procedure, but the results are acceptable. The risk was higher than that for patients with higher body weight in RACHS-1 category 3 and 4. Further investigation to improve the outcome of this high-risk group is needed.  (Circ J 2014; 78: 393–398)