Fetal and pediatric cardiomyopathies are rare disorders with a yearly incident rate of 1.1-1.5 per 100, 000. Hypertrophic and dilated cardiomyopathy are two common forms of cardiomyopathy, characterised by thickened ventricular wall with diastolic dysfunction. The alpha kinase 3 (ALPK3) gene had recently been described to be associated with severe forms of pediatric cardiomyopathy, with phenotypic variations. We describe a case of fetal hydrops that presented on the 3rd trimester, due to severe cardiomyopathy with a ALPK3 gene mutation detected. A 40-year-old, G9P2, consanguineous relationship, with gestational diabetes and hypothyroidism, had a routine growth ultrasound at 32+3 showing fetal ascites. The ultrasound at the fetal medicine unit showed cardiomegaly and hydrops fetalis. Primary investigations for hydrops returned normal. Fetal Echocardiography confirmed cardiomegaly with biventricular hypertrophy and poor contractility, no apparent structural abnormality. Results from genetic testing (QF-PCR and MCA) were normal. The parents were counselled regarding further testing for definitive diagnosis. Interim, cardiac functioning was worsening along with hydrops fetalis needing imminent delivery by Caesarean section. At 33+1 weeks of gestation, a baby boy was born by Caesarean section. At birth weighed 2.2Kg and was transferred to NICU needing support due to impaired cardiac function. Aim of the treatment was to reach around 10Kg in order to have a heart transplant. Unfortunately, at three months of age the cardiac function deteriorated. Meanwhile a homozygous ''likely pathogenic'' variant in the ALPK3 gene was detected on whole-exome sequencing (WES), which have been associated with autosomal recessive cardiomyopathy. The parents were advised of the poor prognosis based on available literature. The decision was made to cease all life support. Parents were found to be carriers of the gene variation and were advised about the recurrence risk. VP22.18 Prenatal diagnosis of ostium secundum-type interatrial communication: a case report