Objectives The purposes of this study were to assess the growth of left heart (LH) structures, to evaluate midterm outcomes, and to define echocardiographic p arameters predictive of increased risk of re-intervention in patients born with aortic coarctation and hypoplasia of LH structures that underwent neonatal coar ctation repair. Background Neonatal coarctation is often associated with hypopla sia of LH structures. Although previous studies have shown that coarctation repa ir can be performed with good results in these neonates, there are little data r egarding growth of the LH structures or outcomes in these patients. Methods Pati ents with isolated coarctation and at least one hypoplastic LH valve (mitral or aortic Z-score < -2) who underwent a neonatal coarctatio n repair were identified. Clinic charts and the latest echocardiograms were revi ewed. Results All 55 patients were alive and well, and no patient had clinical e vidence of mitral stenosis. Three patients (5%) required reintervention. Thirty -eight patients had echocardiograms that demonstrated normal left ventricular(L V) size and function with a follow-up duration of 73 ±19 months (range 3 to 9 years). Both mitral and aortic annulus Z-scores increased significantly: -3.1 ±1.5 to -0.5 ±1.6 (p< 0.001) and -3.5 ±1.9 to 0.7 ±1.6 (p< 0.001), respect ively. Nine patients (24%)-developed LV outflow tract obstruction by echocardi ographic criteria. Conclusions After neonatal coarctation repair with associated LH hypoplasia, LH structures increase substantially in size, and clinical outco mes are excellent at midterm followup. Despite initial annular hypoplasia, the n eed for intervention for mitral or aortic/subaortic stenosis is uncommon. Objectives The purposes of this study were to assess the growth of left heart (LH) structures, to evaluate midterm outcomes, and to define echocardiographic pramers predictive of increased risk of re-intervention in patients born with aortic coarctation and hypoplasia of LH structures that Underwent neonatal coarctation is often associated with hypoplasty of the LH structures. outcomes in these patients. Methods Pati ents with isolated coarctation and at least one hypoplastic LH valve (mitral or aortic Z-score <-2) who underwent a neonatal coarctatio n repair were identified. Clinic charts and the latest echocardiograms were revi ewed. Results All 55 patients were alive and well, and no patient had clinical e vidence of mitral stenosis. Three patients (5%) required r Thirty-eight patients had echocardiograms that demonstrated normal left ventricular (LV) size and function with a follow-up duration of 73 ± 19 months (range 3 to 9 years). Both mitral and aortic annulus Z-scores increased significantly: - Nine patients (24%) - developed LV outflow tract obstruction by echocardiographic criteria. Conclusions After (3.1 ± 1.5 to -0.5 ± 1.6 (p <0.001) and -3.5 ± 1.9 to 0.7 ± 1.6 neonatal coarctation repair with associated LH hypoplasia, LH structures increase substantially in size, and clinical outco mes are excellent at midterm followup. Despite initial annular hypoplasia, the n eed for intervention for mitral or aortic / subaortic stenosis is uncommon.