BACKGROUND: Gestational diabetes mellitus (GDM) and preeclampsia are common complications of pregnancy, for which overweight/obesity is a common risk factor. Both conditions are associated with a two-to-four-fold increase in future incident heart failure, which may be linked to early maladaptive myocardial changes. OBJECTIVE: To determine maternal myocardial structural, functional, and energetic responses to pregnancies complicated by GDM or preeclampsia compared to healthy pregnancies (HP) at third-trimester of pregnancy and 12-months postpartum. STUDY DESIGN: Thirty-eight women with HP, 30 GDM, 20 preeclampsia, 10 nonpregnant controls with overweight (Overweight-NC), and 10 with normal-weight were recruited. Cardiovascular magnetic resonance spectroscopy and imaging were used to define myocardial energetics (phosphocreatine: ATP ratio [PCr/ATP]), left ventricular (LV) volumes, mass, and ejection fraction and global longitudinal shortening (GLS). Pregnancy groups underwent repeat scans 12-months postpartum, nulliparous-controls were assessed once. RESULTS: During third-trimester, compared to HP, women with either GDM or preeclampsia displayed higher BMI, higher LV-mass (HP: 90 [85, 94] g, GDM: 103 [96, 112], Preeclampsia: 118 [111, 125] g; P=.001) and lower PCr/ATP (HP: 2.2 [2.1, 2.4], GDM: 1.9 [1.7, 2], Preeclampsia: 1.9 [1.8, 2.1]; P=.0004) and GLS (HP: 20 [18, 21]%, GDM: 18 [17, 19]%, Preeclampsia: 16 [14, 17]%; P=.01). Post-pregnancy, no group saw significant changes in LV-mass, PCr/ATP, or GLS. There were no significant differences in LV-mass, PCr/ATP or GLS between the GDM and preeclampsia groups during or post-pregnancy. Moreover, the Overweight-NC showed no significant differences in LV-mass (53 [43, 63])g, PCr/ATP (2.0 [1.8, 2.2]), or GLS (-19 [17, 21]%) compared to GDM or preeclampsia groups during or post-pregnancy. CONCLUSION: Women with GDM or preeclampsia exhibit similar myocardial phenotypes during pregnancy with persistent subclinical alterations in LV mass, energetics, and GLS 12-months postpartum. These myocardial alterations are similar to those detected in Overweight-NC, potentially suggesting the myocardial changes may predominantly be driven by overweight/obesity.