Background: Maternal obesity during pregnancy is associated with poorer cardiovascular health (CVH) in children. A strategy to improve CVH in children could be to address preconception maternal obesity by means of a lifestyle intervention. We determined if a preconception lifestyle intervention in women with obesity improved offspring’s CVH, assessed by magnetic resonance imaging (MRI). Methods: We invited children born to women who participated in a randomised controlled trial assessing the effect of a preconception lifestyle intervention in women with obesity. We assessed cardiac structure, function and geometric shape, pulse wave velocity and abdominal fat tissue by MRI. Results: We included 49 of 243 (20.2%) eligible children, 24 girls (49%) girls, mean age 7.1 (0.8) years. Left ventricular ejection fraction was higher in children in the intervention group as compared to children in the control group (63.0% SD 6.18 vs. 58.8% SD 5.77, p = 0.02). Shape analysis showed that intervention was associated with less regional thickening of the interventricular septum and less sphericity. There were no differences in the other outcomes of interest. Conclusion: A preconception lifestyle intervention in women with obesity led to a higher ejection fraction and an altered cardiac shape in their offspring, which might suggest a better CVH. Impact: A preconception lifestyle intervention in women with obesity results in a higher ejection fraction and an altered cardiac shape that may signify better cardiovascular health (CVH) in their children.This is the first experimental human evidence suggesting an effect of a preconception lifestyle intervention in women with obesity on MRI-derived indicators of CVH in their children.Improving maternal preconception health might prevent some of the detrimental consequences of maternal obesity on CVH in their children.