OBJECTIVES: to evaluate the structural and functional heart abnormalities in women with mitral regurgitation during pregnancy. INTRODUCTION: Women with mitral regurgitation progress well during pregnancy. However, the effects on the heart of the association between pregnancy and mitral regurgitation are not well established. METHODS: This is a case-control, longitudinal prospective study. Echocardiograms were performed in 18 women with mitral regurgitation at the 12th and 36th week of pregnancy and on the 45th day of the puerperium. Twelve age-matched healthy and pregnant women were included as controls and underwent the same evaluation as the study group. RESULTS: Compared with controls, women with mitral regurgitation presented increased left cardiac chambers in all evaluations. Increasing left atrium during pregnancy occurred only in the mitral regurgitation group. At the end of the puerperium, women with mitral regurgitation showed persistent enlargement of the left atrium compared with the beginning of pregnancy (5.0 ± 1.1 cm vs 4.6 ± 0.9 cm; p<0.05). Reduced left ventricular relative wall thickness (0.13 ± 0.02 vs 0.16 ± 0.02; p<0.05) and an increased peak of afterload (278 ± 55 g/cm² vs 207 ± 28 g/cm²;p<0.05) was still observed on the 45th day after delivery in the mitral regurgitation group compared with controls. CONCLUSIONS: Pregnancy causes unfavorable structural alterations in women with mitral regurgitation that are associated with an aggravation of the hemodynamic overload.