Background: Children with congenital heart disease (CHD) have been reported to show significant growth retardation both prenataly and postnatally. Cyanotic CHDs in children commonly cause more pronounced growth retardation in comparison with acyanotic CHDs. Chronic hypoxemia has been suggested as the cause of poor growth in these patients. Interruption of GH / IGF-1 axis decreased appetite due to hypoxemia leading to insufficient food intake and increased energy consumption may be a cause of the increased growth failure in patients with cyanotic CHDs. The relationship between cyanotic CHDs, malnutrition and growth retardation is well documented. The aim of this study was to investigate the effects of cyanosis and chronic hypoxia on plasma level of insulin-like growth factor-1 and to examine the prevalence of elevated TSH in the patients with cyanotic congenital heart diseases. Methods: This study had two groups; Cases group: included 30 patients with cyanotic CHD, who admitted to the Pediatric Cardiology Outpatient Clinic of benha university hospital, Another 35 patients, who admitted to the Pediatric Outpatient Clinic with several complaints, including headache or abdominal discomfort or for scheduled vaccination visits were included in the control group. Results: The mean age in the studied cases was 24.1±13.8 months, ranged from 3-60 months, and consists of 18 males and 12 females, the mean age in the control group was 21.8±12.6 months, ranged from 3-60 months, and consists of 18 males and 17 females. There was no statistical difference between cases and control groups regarding age, or sex. The most frequent diagnosis in our study, was TOF (46.7%), then TGA (40%), All the studied cases had history of previous hospital admission, and 40% of cases had history of previous PICU admission.There was statistical significant difference between studied groups regarding anthropometric measures, as weight, height and BMI centiles were statistically lower in cases group, while there was no significant difference between groups regarding head circumference. There was Hb and WBCs were statistically higher in cases group, while platelets were statistically lower in cases group, compared to control group (p < 0.001). Serum urea and creatinine were significantly higher in cases group compared to control group (p < 0.001, and p=0.42, respectively). While there was no significant difference between groups regarding random blood sugar, serum Ca , serum K, serum Na and serum phosphorus. Insulin-Like Growth Factor (IGF-1) was statistically higher in cases group (60.4±24.3 ng/mL), compared to control group (141.2±45.6 ng/mL), p < 0.001.There was no significant difference between groups regarding thyroid function tests. Seven children (23.3%) in cases group had subclinical hypothyroidism, while 4 children (11.4%) of control group had subclinical hypothyroidism, but no significant difference were found.There was a significant difference between IGF-1 regarding sex as it was significantly lower in males (48±12.95 ng/mL) compared to females (79±25.43 ng/mL), p= 0.002. And it was significantly lower in patients with previous history of PICU admission (52.33±25.13 ng/mL), compared to patients without previous history of PICU admission (72.5±17.12 ng/mL), 0.014. While there was no significant difference between different etiologies of cyanotic heart diseases regarding IGF-1, p=0.45. There was a significant positive correlation between IGF-1 and (BMI and platelets), and there was a significant negative correlation between IGF-1 and (Hb level and serum creatinine). While there was no significant correlation between IGF-1 and other parameters. Conclusion: Cyanotic CHDs in children commonly cause more pronounced growth retardation. IGF-1 was decreased in patients with cyanotic CHD, also, IGF-1 correlated with growth parameters. For this reason, we believe that chronic hypoxia plays a significant role in the pathogenesis of malnutrition through GH/IGF-I axis.