▁the ▁right ▁side ▁of ▁the ▁heart ; ▁or ▁the ▁opposite , ▁depending ▁on ▁whether ▁the ▁left ▁or ▁right ▁at rium ▁has ▁the ▁higher ▁blood ▁pressure . ▁In ▁the ▁absence ▁of ▁other ▁heart ▁defect s , ▁the ▁left ▁at rium ▁has ▁the ▁higher ▁pressure . ▁This ▁can ▁lead ▁to ▁lower - than - normal ▁o xygen ▁levels ▁in ▁the ▁ar ter ial ▁blood ▁that ▁supplies ▁the ▁brain , ▁org ans , ▁and ▁t issues . ▁However , ▁an ▁AS D ▁may ▁not ▁produce ▁notice able ▁signs ▁or ▁sympt oms , ▁especially ▁if ▁the ▁defect ▁is ▁small . ▁ ▁Also , ▁in ▁terms ▁of ▁health ▁ris ks , ▁people ▁who ▁have ▁had ▁a ▁crypt ogen ic ▁stroke ▁are ▁more ▁likely ▁to ▁have ▁a ▁P FO ▁than ▁the ▁general ▁population . ▁ ▁A ▁card iac ▁sh unt ▁is ▁the ▁presence ▁of ▁a ▁net ▁flow ▁of ▁blood ▁through ▁a ▁defect , ▁either ▁from ▁left ▁to ▁right ▁or ▁right ▁to ▁left . ▁ ▁The ▁amount ▁of ▁sh un ting ▁present , ▁if ▁any , ▁determ ines ▁the ▁hem od ynamic ▁significance ▁of ▁the ▁AS D . ▁A ▁right - to - left - sh unt ▁results ▁in ▁ven ous ▁blood ▁entering ▁the ▁left ▁side ▁of ▁the ▁heart ▁and ▁into ▁the ▁ar ter ial ▁circul ation ▁without ▁passing ▁through ▁the ▁pul mon ary ▁circul ation ▁to ▁be ▁o xygen ated . ▁This ▁may ▁result ▁in ▁the ▁clin ical ▁finding ▁of ▁cy anos is , ▁the ▁presence ▁of ▁bl u ish - color ed ▁skin , ▁especially ▁of ▁the ▁lips