Proximal interruption of the pulmonary artery (PA) is a rare congenital vascular anomaly with an estimated prevalence of 1 in 200,000 young adults. Patients with isolated proximal interruption of the right PA are usually asymptomatic but can present with breathlessness, haemoptysis, recurrent chest infections, pulmonary hypertension or respiratory failure. Such symptoms may be unmasked by pregnancy or at high altitude. We present a case of an isolated interruption of the right PA in a 29-year-old male with a history of cough and breathlessness, requiring hospitalization and ventilator support after travel to a hilly region. Laboratory reports showed normal haemogram and normal renal and liver function tests. Screening test for deep vein thrombosis/pulmonary embolism were negative. Echocardiogram was normal and did not show any evidence of elevated PA pressures. All serial X-rays were reviewed and showed one consistent finding: right lung volume loss with transmediastinal herniation of the left lung to the right side. We discuss the radiological and clinical features along with treatment options for the condition.