Congenital heart defects in chick embryos subjected to temperature variations.

• Several epidemiological studies" have shown a positive correlation between viral diseases early in pregnancy and congenital heart disease in human beings. Since viral diseases are accompanied commonly by fever, it was considered important to investigate the effect of high temperature alone on the development of the heart in chick embryos. It was also thought that incubation at low temperature might delay the development of certain embryonic tissues, particularly the heart. In the very few experiments in which the effect of low temperature on development has been studied,' congenital heart defects were not mentioned. The results described here indicate that high temperature does not induce cardiac abnormalities in chicks but that low temperature does.