A 54 year-old woman with Noonan Syndrome presented with an acute anterolateral ST elevation myocardial infarction two weeks post septal myectomy and heparin exposure, on the background of known normal coronary arteries. Coronary angiography revealed acute thrombosis of the left main, left anterior descending and left circumflex arteries, which was successfully treated by percutaneous coronary intervention with overlapping bare metal stents. A positive heparin induced platelet antibody test and dramatic fall in platelet count confirmed the diagnosis of heparin induced thrombocytopaenia with thrombosis (HITTS) as the underlying diagnosis. This represents the first documented case of HITTS induced left main coronary artery thrombosis and occlusion.