Background: Pulmonary artery sarcoma is a rare tumor with a poor prognosis. Case Report: We report the case of a 64-year-old man with an intimal pulmonary artery sarcoma presenting with severe high oxygen flow-demanding dyspnea and weight loss of 12 kg in the last 6 months. On echocardiography, right heart insufficiency, markedly elevated right ventricular pressure, a pressure gradient along the right outflow tract, and a tumor mass adherent to the wall of the truncus pulmonalis were detected. The tentative diagnosis by echocardiographic findings was pulmonary artery sarcoma. Computed tomography of the thorax and 18-fluorodeoxyglucose positron emission tomography showed an advanced local tumor manifestation. Surgical resection of the tumor to improve hemodynamics confirmed the diagnosis. Conclusions: Pulmonary artery sarcoma should be considered as a rare differential diagnosis in patients with dyspnea due to right heart failure, particular in the case of additional weight loss, and echocardiographic examination is a useful first diagnostic approach in establishing the diagnosis.