Ventilation-perfusion (V/Q) lung scintigraphy has been a popular diagnostic test for evaluation of pulmonary thromboembolism (PE) for almost 40 years. Despite the validation of V/Q scintigraphy, it is important to remember that there are causes of unmatched perfusion defects that are not due to PE. Here, we describe a very rare case of right main pulmonary artery atresia with left circumflex coronary collaterals supplying the affected lung in an adult patient diagnosed by V/Q scan and CT angiography (CTA). Lung perfusion scan disclosed the total absence of perfusion in the right lung, while ventilation scan disclosed decreased size of the right lung with diminished but homogeneous radioactivity distribution. CTA showed occlusion of the right main pulmonary artery with no evidence of embolus. Three-dimensional reconstruction demonstrated large, tortuous collateral vessels arising from the left circumflex coronary branch to the affected lung indicating collaterals formed from the coronary circulation to the pulmonary circulation. We highlight that demonstrations on V/Q scintigraphy in such cases should be interpreted with caution.