The pre-existing compression of the left ventricle in congenital diaphragmatic hernia (CDH) could be aggravated by the amplified lung growth after fetoscopic endoluminal tracheal occlusion (FETO). Our aim was to document left ventricular (LV) size and function in fetuses with isolated left-sided CDH and to document the effect of FETO on the fetal heart.We determined cardiac axis, LV diameters, ejection fraction, shortening fraction, mitral E/A index and myocardial performance index (MPI) in 27 fetuses with isolated left-sided CDH, and compared these with values in a reference population (n = 117). In fetuses with severe CDH that subsequently underwent FETO and/or reversal of occlusion, additional measurements were obtained 24 h before and after each fetal intervention. We recorded fetal el...