Purpose: The purpose of this study was to examine and analyze the post operative fasting period of neonates in the intensive care unit (ICU) after receiving open heart surgery in order to provide optimal nutrition support for these neonates. The variables included biochemical nutrition indexes (albumin, total lymphocyte count, total cholesterol) and patient outcomes (duration of mechanical ventilation, ICU stay, hospital stay, infectious complication). Methods: The participants were 124 neonates in ICU after receiving open heart surgery, and the design of this study was to investigate their post operative fasting period retrospectively to analyze the biochemical nutrition indexes and patient outcomes according to post operative fasting period. Results: The results for 4 groups according to post operative fasting period showed that the group with less 48 hours of fasting had the best biochemical nutrition indexes and patient outcomes, followed by the 48-72 hour group, the 72-144 hour group, and the over 144 hour group. Conclusion: The results indicate that for new born babies receiving open heart surgery, the period of fasting after the operation should be minimized and tube feeding should be started as soon as possible.