Ectopia cordis in the chick embryo heart: an experimental study.

Ectopia cordis was observed during a study on the effects of a calcium antagonist (verapamil) on chicken embryo heart development. Experimental procedures, carried out at 60 hours of incubation, included placement of windows in eggs, injection of verapamil or saline, and the removal of ovalbumen from eggs. Fluid removal caused a downward displacement of the embryo and helped separate the embryo and its membranes from the shell membranes. Ectopia cordis was only observed in experiments involving fluid removal. One exception, the appearance of one ectopic heart in a window-only experiment (no fluid removed), remains unexplained. The movements of fluids, brought about by the withdrawal of ovalbumen from eggs, and the subsequent effects of such movements on the positioning of embryos seemed to be the most important factor in the genesis of ectopia cordis. Also observed in fluid removal experiments were asymmetric circulations, abnormal embryonic flexion, and several embryos whose positions were rotated. These abnormalities were probably related to fluid removal and/or ectopia cordis.