Aim: To evaluate the modified myocardial performance index (Mod-MPI) in foetuses with growth restriction and compare this index with appropriate for gestational age foetuses. Material and methods: A prospective cross-sectional case-control study was conducted involving 76 singleton foetuses between 24 and 34 weeks of gestation divided into three groups (24 appropriate growth foetuses, 30 foetuses with estimated weight between the 3 rd and 10 th percentiles and 22 foetuses with estimated weight < 3 rd percentile, according to the Hadlock table). The Mod-MPI was obtained in the plane of the four chamber view, and the spectral Doppler sample volume was placed in the lateral wall of the aorta, close to the mitral valve. Doppler of umbilical artery was normal in all cases. Analysis of variance (ANOVA) was used to compare the groups and the intra-class correlation coefficient (ICC) was used to assess intra-and inter-observer reproducibility. Results: The mean Mod-MPI in the groups of appropriate for gestational age, estimated weight between the 3 rd and 10 th percentiles, and estimated weight < 3 rd percentile was 0.32 ± 0.05, 0.35 ± 0.05 and 0.36 ± 0.06, respectively; there was no statistical difference between the groups (p = 0.072). There was good intra-and inter-observer reproducibility (ICC = 0.726 and 0.760, respectively). Conclusion: Mod-MPI was not significantly different between foetuses appropriate for gestational age and those with growth restriction. Mod-MPI proved to be a feasible and reproducible technique.