Thyroid disease in cardiac surgery is a challenge in regards to patient management especially post­operative as a result of two systems, endocrine and cardiovascular systems, working in antagonism. In this case review, we narrate a unique case of a 65­year­old African female with severe mitral regurgitation and incidental atrial septal defect who underwent mitral valve replacement and atrial septal defect closure. She later developed poor cardiac function post operatively owing to initially unrecognised subclinical hypothyroidism that was not being treated. This worsened post cardiopulmonary bypass and the setting of acute severe physiological stress secondary to cardiac surgery. On administration of thyroxine 100mcg daily, she improved haemodynamic and was later discharged. A discussion is made in focus to cardiac surgery in the background of hypothyroidism. Various literature reviews provide useful information in this field. However further studies on African based population are recommended to collaborate the existing data or even demonstrate variations in this population.