High-altitude environments with low oxygen pressure can cause serious damage to the heart and lungs, especially in young people. In two cases of young men who lived for several months at altitudes above 4,300 m, chest pain, shortness of breath, loss of consciousness and temporary deterioration of vision gradually appeared. Both persons had a significantly reduced oxygen saturation (80 and 82%) after arriving at lower altitudes. Echocardiography showed enlargement of the right heart and increased pulmonary artery pressure (55 and 56 mmHg). A CT scan confirmed enlargement of the right heart and enlargement of the pulmonary artery. The diagnosis of high-altitude pulmonary hypertension was established after other causes had been ruled out. The basic treatment is leaving the high mountain environment and early diagnosis.