Extrinsic left main coronary artery (LMCA) compression is well described in patients with severe pulmonary dilatation secondary to atrial septal defect, idiopathic pulmonary artery hypertension, and eisenmengerized patent ductus arteriosus. An inferiorly displaced origin of LMCA closer to the left coronary sinus and a dilated pulmonary artery (PA) trunk twice as much as aortic trunk increases risk of extrinsic compression. Such patients are prone to left ventricular ischaemia, malignant ventricular arrhythmia, and sudden cardiac death. A 20-year-old girl presented with gradually worsening exertional dyspnoea for the last 5 years was diagnosed to have tetralogy of Fallot with absent pulmonary valve (TOF-APV). After undergoing intra-cardiac repair with bioprosthetic pulmonary valve implantation, she developed a broad complex right bundle branch block with right precordial Q waves (qRBBB), new-onset left ventricular dysfunction, acute decompensated heart failure, and elevated serum cardiac enzymes. Coronary angiogram and intravascular ultrasound examination showed a critically narrowed slit-like LMCA ostium. Percutaneous stenting of LMCA saw resolution of qRBBB and improvement in left ventricle function, after which patient stabilized and could be weaned off ventilatory support. Left main coronary artery compression after surgical pulmonary valve replacement in TOF-APV occurring few days after the operation may pose diagnostic and therapeutic challenges. Exact mechanism for post-operative compression is not known. It can be hypothesized that the ionotropic agents used in post-operative period, or change in the geometric relationships of pulmonary artery and LMCA due to pulmonary valve implantation, brought out the compression. A case for prophylactic PA size reduction can be made to avoid the possibility of LMCA compression.