About 40% of individuals with Down syndrome suffers from congenital heart diseases. Atrioventricular septal defect is the most common cardiac anomaly. Other common heart diseases are: - Ventricular septal defect - Mitral valve anomalies - Tetralogy of Fallot - Patent ductus arteriosus Reference: https://en.wikipedia.org/wiki/Down_syndrome#Heart Image via: https://medicalxpress.com/news/2014-10-clues-genetics-congenital-heart-defects.html