▁g ases ▁through ▁the ▁l ungs ▁to ▁be ▁ex h aled . ▁If ▁some ▁of ▁the ▁in ert ▁gas - lad en ▁blood ▁passes ▁through ▁the ▁P FO , ▁it ▁avoid s ▁the ▁l ungs ▁and ▁the ▁in ert ▁gas ▁is ▁more ▁likely ▁to ▁form ▁large ▁b ub bles ▁in ▁the ▁ar ter ial ▁blood ▁stream ▁causing ▁decom pression ▁sick ness . ▁ ▁Eisen men ger ' s ▁synd rome ▁ ▁If ▁a ▁net ▁flow ▁of ▁blood ▁exists ▁from ▁the ▁left ▁at rium ▁to ▁the ▁right ▁at rium , ▁called ▁a ▁left - to - right ▁sh unt , ▁then ▁an ▁increase ▁in ▁the ▁blood ▁flow ▁through ▁the ▁l ungs ▁happens . ▁ ▁Initial ly , ▁this ▁increased ▁blood ▁flow ▁is ▁asympt om atic , ▁but ▁if ▁it ▁pers ists , ▁the ▁pul mon ary ▁blood ▁vessels ▁may ▁st iff en , ▁causing ▁pul mon ary ▁hy pert ension , ▁which ▁increases ▁the ▁press ures ▁in ▁the ▁right ▁side ▁of ▁the ▁heart , ▁leading ▁to ▁the ▁revers al ▁of ▁the ▁sh unt ▁into ▁a ▁right - to - left ▁sh unt . ▁ ▁Re vers al ▁of ▁the ▁sh unt ▁occurs , ▁and ▁the ▁blood ▁ ▁flow ing ▁in ▁the ▁opposite ▁direction ▁through ▁the ▁AS D ▁is ▁called ▁Eisen men ger ' s ▁synd rome , ▁a ▁rare ▁and ▁late ▁comp lication ▁of ▁an ▁AS D . ▁ ▁Par ado x ical ▁em bol us ▁Ven ous ▁th rom bus ▁( cl ots ▁in ▁the ▁ve ins ) ▁are ▁quite ▁common . ▁