We present a case report of a pregnant woman with increased risk for trisomy 21 at first-trimester screening, assessed by ultrasonography, that was sent to our hospital. Amniocentesis was performed at 14 weeks and 2 days to obtain foetal karyotype that was normal (46,XX). At 19 weeks and 1 day, foetal hydrops associated with cardiac malformation was detected by routine scan. Foetal echocardiogram revealed a complete auriculoventricular septal defect, non-compacted myocardium, and a bradycardia of 70–90 beats per minute, which lead to the suspicion of left isomerism. Foetal death occurred at 20 weeks and 3 days. Autopsy was consistent with the prenatal diagnosis.