SummaryAuthor emphasizes the importance of the bulged pulmonary artery for the diagnostic of some heart diseases.He shortly describes the different heart diseases which show this roentgenologic abnormality and notices their most pathognomonic symptoms. Some investigations as catheterisation of the heart cavities, angiocardiography, rebreathing test and ratio of oxygen utilization (Bing’s test) are specially valuable for diagnosis.At last, a practical classification of the heart diseases with bulged pulmonary artery is proposed.