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Monosomy 21 is a rare chromosomal abnormality, with only nine cases reported in the literature. Affected infants display multiple dysmorphic features as well as skeletal, ocular, pulmonary, cardiac, renal, and genitourinary abnormalities. All monosomies are lethal except monosomy 21, but not all monosomy 21 fetuses survive to term. This report describes the echocardiographic findings and the congenital heart defects associated with the third case of molecularly confirmed full monosomy 21 in the literature. The cardiac defects included a mildly hypoplastic and hypertrophied left ventricle, a large ostium secundum atrial septal defect, a small anterior muscular ventricular septal defect, an interrupted inferior vena cava with azygos continuation, a parachute mitral valve, a bicuspid aortic valve, and a tortuous descending aorta. It also is the first description of a left pulmonary artery aneurysm and decreased left ventricular function as a component in the spectrum of defects found in full monosomy 21. [ABSTRACT FROM AUTHOR]