What Is Hypoplastic Left Heart Syndrome (HLHS)?. Hypoplastic left heart syndrome (HLHS) is a rare birth defect of a baby's heart. The left side of the heart ...[SkiptoContent]SharetoFacebookSharetoTwitterSharetoPinterestShareviaEmailKidsHealth/forParents/HypoplasticLeftHeartSyndrome(HLHS)HypoplasticLeftHeartSyndrome(HLHS)Reviewedby:MichaelA.Bingler,MDLargertextsizeLargetextsizeRegulartextsizePrintenespañolSíndromedecorazónizquierdohipoplásicoWhatIsHypoplasticLeftHeartSyndrome(HLHS)?Hypoplasticleftheartsyndrome(HLHS)isararebirthdefectofababy'sheart.Theleftsideoftheheartdoesn'tgrowasitshould,makingitsmallerandweakerthannormal.Theleftsideoftheheartissupposedtopumpbloodouttothebody.Butababy'sheartwithHLHScan'tdothejob.Thismakesababyverysick.Withoutmedicinesandaseriesofthreesurgeriestorebuildtheheart,babieswithHLHSwon'tsurvive.Theleftsideoftheheartcan'tbefixed,sothegoalofthesurgeriesistorebuildpartsoftheheartand"redirect"thewaybloodflowstoandfromthebody.Soonafterbirth,ababywithHLHSneedsaround-the-clockcareinahospitalforthefirstweeksormonthsoflife.HowDoestheHeartWork?Theheartisamusclethatpumpsblood.Itactsliketwopumpsinone.Thepumpsarecalledventriclesandeachhasanimportantjob:Therightventriclegetsbloodfromthebodyandpumpsitoutthepulmonaryarterytothelungs.Inthelungs,bloodfillsupwithoxygenandgetsridofcarbondioxide.Theleftventriclegetsthebloodfromthelungsandpumpsitoutthroughtheaortatothebody.Becauseitpumpsbloodtotheentirebody,theleftventricleisastrongerpumpthantherightventricle.WhatHappensinHypoplasticLeftHeartSyndrome?Withhypoplasticleftheartsyndrome:Theleftventricleandaortaaretoosmalltopumpenoughbloodtothebody.Therightventricle,whichisonlysupposedtopumpbloodtothelungs,pumpsbloodtothelungsandthebodythroughanextrapathwaycalledapatentductusarteriosis(PDA).Thatmeanstherightventriclegetsoverworked.BabieswithHLHSarealmostalwaysbornwithanatrialseptaldefect(ASD).Thisisaholeintheupperpartoftheheart.Itletsbloodwithoxygenmixwithbloodlowonoxygen.Thentherightventriclepumpsthebloodtothelung