The conus with no great artery.

In three patients with complex cyanotic congenital heart disease, the conus was found to have no arterial outlet. The semilunar valves were at similar, caudad levels, and there was malposition of the great arteries. The aorta was related to the body--not the outflow portion--of the right ventricle in two patients with transposition and to the body of the left ventricle in one child with single ventricle. These cases confirm the independent embryological segregation of the conus and the truncus. Failure to recognize this condition can lead to erroneous relationship diagnoses and may adversely influence surgical decisions.