Background and Aims: Infants born to mothers with gestational diabetes mellitus (GDM) have impaired myocardial performance and are at risk of pulmonary hypertension. We aimed to assess myocardial deformation and left ventricular (LV) rotational mechanics in this population. Methods: We studied 40 infants of mothers with GDM and 40 control infants. Three echocardiograms were carried out over the first 3 days after birth. Results: GDM infants had a lower gestation at birth and a thicker septal wall, a higher LV eccentricity index (indicating septal bowing), and a lower PAATi (indicating higher pulmonary vascular resistance) (all p < 0.05). GDM infants had lower LV strain, systolic and early diastolic strain rates, lower right ventricular (RV) strain, and early diastolic strain rates over the study period (all p < 0.05). By day 3, GDM infants had higher twist, torsion, and higher LV twist and untwist rates (all p < 0.05). GDM status was an independent predictor of LV and RV function and pulmonary vascular resistance (p < 0.01). Conclusion: Infants of mothers with GDM demonstrate important changes in myocardial function in addition to pulmonary vascular resistance that do not resolve by hospital discharge. The observed LV twist increase in GDM infants may be a compensatory mechanism for the lower longitudinal function in this cohort.