Hypothyroidism in patients undergoing congenital heart defect surgery is known to be possible. This generally temporary condition can progress as it involves yet other factors, increasing the patients’ time to heal. The case presented here is that of a 5-month-old girl who was dependent in the long term on mechanical ventilation following cardiac surgery. After having been diagnosed with hypothyroidism, she was extubated on the fourth day of her hormone replacement therapy, and discharged from hospital on the tenth day.