We examined the eustachian valve and the limbus of the foramen ovale in 42 hearts with hypoplastic left heart syndrome (HLHS) and in 16 normal hearts. In HLHS, only 4.8% of the eustachian valves were moderately to well developed, whereas the remaining 95.2% were abnormal (p < 0.001): 92.9% of the eustachian valves were absent or markedly hypoplastic, and 2.4% had an abnormally redundant and enlarged eustachian valve. The eustachian valve was well developed in 87.5% of normal hearts. In addition, the lesser development of the eustachian valve seemed to correlate with lesser development of the left side of the heart. The limbus was well developed in 100% of the normal hearts and moderately to well developed in only 33.3% of the HLHS group (p < 0.001). Most hearts in the HLHS group had marked hypoplasia of the limbus, which was rotated and deviated so as to be close to the superior vena caval entrance.