A two–year old boy present with episodes of becoming dusky. On examination, there was central cyanosis and clubbing. There was no pallor, oedema or respiratory distress. The heart was normal sized with a parasternal heave. A systolic thrill was palpable over the left middle sternal border. First heart sound was normal and only the aortic component was audible in the second heart sound. Liver was not enlarged – What would be the likely diagnosis –