Abstract Background Maternal preeclampsia (PE) has been associated with an increased risk of a variety of congenital heart defects in the infant. Whether PE also confers an increased risk of subtle structural and functional cardiac deficits is unknown. Purpose We investigated whether left ventricular dimensions and systolic function differed among infants of mothers with PE, compared to infants born after uncomplicated pregnancies. Method Systematic transthoracic echocardiography (TTE) was performed in neonates included in a population-based study in the period 2016–2018 (n=25,000). TTE was preferably performed within 14 days of birth. Left ventricular (LV) posterior wall end-diastolic thickness (LVPWd), interventricular septum end-diastole thickness (IVSd), LV internal diameter in end-diastole and end-systole (LVIDd and LVIDs), LV ejection fraction (LVEF) and fractional shortening (FS) were assessed. Information on maternal PE (ICD-10 codes DO140–142 and DO159) was retrieved from an obstetric database. Using linear regression in a sample of echocardiograms, we compared the LV structure and function adjusted for maternal age; gestational age; sex; weight and length. Results In total, 447 infants were exposed to PE, and 7,178 were born to uncomplicated pregnancies (Table). In infants of PE mothers, we found significantly larger LVPWd and IVSd (0.18 mm, 95% CI [0.14; 0.22], p<0.001 and 0.06 mm, 95% CI [0.02; 0.10], p=0.001, resp.) and LVIDd as LVIDs were significantly smaller (−0.15 mm, 95% CI [−0.29; −0.01], p=0.032 and −0.16 mm 95% CI [−0.28; −0.04], p=0.009, resp.) compared to infants of non-PE mothers. We found no differences in systolic function. LV measures in PE and non-PE infants Parameter Infants of PE mothers, Infants of non-PE mothers, p-value Estimate* [95% CI] p-value mean [± SD] (n=447) mean [± SD] (n=7,178) Left Ventricular Posterior Wall in end-Diastole, LVPWd (mm) 2.20 [±0.58] 2.07 [±0.40] <0.001 0.18 [0.14; 0.22] <0.001 Interventricular Septum in end-Diastole, IVSd (mm) 2.53 [±0.52] 2.55 [±0.41] 0.562 0.06 [0.02; 0.10] 0.001 Left Ventricular Internal Diameter in end-Diastole, LVIDd (mm) 19.35 [±2.00] 20.10 [±1.41] <0.001 −0.15 [−0.29; −0.01] 0.032 Left Ventricular Internal Diameter in end-Diastole, LVIDs (mm) 13.13 [±1.43] 13.65 [±1.79] <0.001 −0.16 [−0.28; −0.04] 0.009 Fractional Shortening, FS (%) 32.10 [±4.07] 32.11 [±3.86] 0.937 0.26 [−0.11; 0.63] 0.168 Left Ventricular Ejection Fraction, LVEF (%) 63.19 [±5.61] 63.09 [±5.30] 0.690 0.34 [−0.17; 0.85] 0.192 *Adjusted for maternal age; gestational age; sex; weight and length. Conclusion In the largest population-based group of neonates to date, we showed that infants born to PE mothers compared to infants of non-PE mothers had significantly thicker left ventricular myocardium, and reduced left ventricular volumes. However, PE was not associated with altered systolic function. Our results might reflect an adaption of the fetal heart to the increased resistance in the placental arteries in PE mothers, and a secondary increased left ventricular afterload. Acknowledgement/Funding Danish Heart Association, Danish Children's Heart Foundation, Candy's Found., Toyota Found., Herlev-Gentofte Hospital Research Found., Lundbeck Found.