We describe a unique case of congenital absence of a right pulmonary artery presenting in a patient of advanced age and initially misdiagnosed as coronary artery disease. Perfusion of the affected lung was accomplished via anomalous collaterals from right and left circumflex coronary arteries which induced myocardial ischemia, as demonstrated by myocardial perfusion scan. To our knowledge there are only three reports in the international literature, describing unilateral pulmonary artery agenesis with the coronary artery supplying the abnormal lung. All these reports described that the existence of such vessels does not affect the myocardial perfusion. However, here we describe, to our knowledge, for the first time that in a patient with unilateral pulmonary artery agenesis, the existence of collaterals from the coronary arteries to the affected lung can actually have a negative effect in myocardial perfusion and can induce myocardial ischemia. In conclusion, clinicians should be aware of the possibility of undiagnosed cases of unilateral pulmonary artery agenesis presenting with chest pain in advanced age.