Background: Congenital heart diseases are the most com-mon type of congenital malformations. Some of them may pass unnoticeable in the first days or maybe years of life, but the others are pretty serious and life-threatening due to major malformations that lead to the mixing of oxygenated and de-oxygenated blood. Most of these cases are not repairable and require separating the venous and arterial blood to help improve oxygen saturation. Aim of Study: The aim of the study is to evaluate the mid and long-term effects of left MBT shunt after bidirectional cavopulmonary shunt. Patients and Methods: A retrospective cohort study was conducted on 20 patients who underwent mBTS after BDG. We evaluated the mid and long-term effects of mBTS in those patients especially SpO2 and echocardiographic findings. The study considered the ethical principles of the Helsinki Declara-tion approval from the research ethics committee at our institu-tion (MS 510/2023). Results: There was a significant increase in postoperative SpO2 in comparison to preoperative SpO2 (p<0.001) with a mean difference of 20.95%. Conclusion: Congenital cyanotic heart diseases represent a life-threatening condition where the main problem is desatura-tion due to the mixing of arterial and venous blood. BDG is a step to separate the oxygenated and deoxygenated blood. But later on, oxygen saturation continues to decline and further in-tervention is needed. In this study, we found that mBTS pro-vides a post-operative significant increase in oxygen saturation in a wide group of those patients even who are not candidates for other operations without significant complications.