Pulmonary arterial hypertension (PAH) is a rare and incurable disease, related to right ventricle overload and failure, which are late consequences of asymptomatic progressive pulmonary vascular occlusion. The clinical approach requires: a high clinical suspicion; the detection and confirmation of PAH by echo-Doppler and right heart catheterisation; identification of an etiology; assessment of functionality and life expectancy; and reversibility testing. We present the case of a 68-year-old male patient presenting with progressive fatigability and shortness of breath, abnormal heart beats in the last 4 years, aggravated in the last year. Clinical findings showed signs of cardiac failure. Multiple echocardiographies demonstrated right atrial and right ventricular dilatation, with severe PAH, subsequent severe pulmonary and tricuspid regurgitation, mild mitral and aortic regurgitation and efficient left ventricular function. Subsequent cardiac catheterization confirms severe PAH, excludes VSD, and sees a left-to-right shunt but an ASD could not be anatomically localized. Left ventricular function and the coronary arteries were normal. Transesophageal echocardiography demonstrated an ASD sinus venosus with bidirectional shunt associated with partial abnormal in pulmonary venous drainage, with right supranumery pulmonary vein with drainage in the sinus venosus, the upper and inferior right pulmonary veins flowing into the right atrium, the upper and inferior left pulmonary veins Bowing into the left atrium, associated to important superior and inferior vena cava dilatation. The patient receives treatment for right heart failure, oral anticoagulation, antiarrhythmic drugs, cardio-pulmonary rehabilitation is initiated and he is referred to a center specialised in PAH, for bosentan treatment. In this patient, it is surprising that even born with a potentially cyanogenic congenital heart disease, his condition is discovered at an advanced age on the edge for evolution towards an Eisenmenger Syndrome, being fairly asymptomatic until the last year when he receives treatment for left heart failure.