Transitional atrioventricular (AV) septal defects are uncommon congenital heart defects, and diagnosis is usually made in childhood. We present the case of intermediate AV canal diagnosed in a man referring to cardiological examination for the first time in his life at the age of fifty for exertional dyspnea. The absence of medical examination or execution of electrocardiogram or echocardiogram in childhood or in youth and the very late appearance of symptoms lead to a late diagnosis of this congenital heart disease (CHD). This case underlines the importance of including CHD in the differential diagnosis of symptoms such as chronic dyspnea, also in adulthood.