In this Journal, Lange et al. describe the use of exerciseechocardiography to identify pulmonary hypertension in thepresence of an atrial septal defect (ASD) [1].Atrial septal defectAn ASD is a relatively common congenital heart diseasewith a birth prevalence of 1.6 per 1000 live births, and aprobabilityofsurvivalintoadulthoodof97%[2,3].Differenttypes of ASDs exist, and the secundum type, located at thefossa ovalis, is the most common (75 %) [4]. An ASD ischaracterised by a left-to-right shunt with volume overloadof the right heart and pulmonary overcirculation. This mightresult in arrhythmias, right heart failure, pulmonary arterialhypertension, and paradoxical embolism, the last mentioneddue to a right-to-left shunt. Echocardiography is the primarydiagnostic technique, and cardiac catheterisation is requiredin cases of a suspected increase in pulmonary artery pres-sure (PAP). Indication for ASD closure is the presence of asignificant shunt with signs of right ventricular volumeoverload without the presence of a severely increased pulmo-nary vascular resistance (PVR) ( 50 mmHg withorwithout additionalfindings[7].Exercise echocardiographyis not recommended by the current PH guideline [7]. Inaddition, exercise causes an increase in mean PAP of up to3 mmHg per 1 l/min increase in cardiac output in healthyindividuals, and this is related to age and gender [9, 10]. Thedefinite diagnosis of PAH should always be confirmed byright heart catheterisation.Pulmonary hypertension and ASDPulmonary arterial hypertension is noted in 9 to 35 % ofpatient with a secundum type ASD, both open and closed[11, 12]. The definition of PH differs among the differentepidemiological studies. Predictors for the occurrence ofPAH are age, size of the defect, non-closed status, andfemale sex [12, 13]. Pulmonary vascular disease related tothe systemic-to-pulmonary shunt might be prevented byearly correction of the defect in most patients. The windowof opportunity for correction and prevention of PAH islesionspecific(pre-orpost-tricuspid)andpulmonaryvascular