A detailed examination of 247 spontaneously aborted foetuses, under the age of 24 weeks gestation, showed 38 instances of cardiac malformation (15.4%). Very early specimens were not included. There was a bimodal relationship with maternal age and parity and a higher incidence in summer conceptions, but there was no apparent association with maternal blood groups. There were more male foetuses and they had proportionately more malformed hearts than the females. There was a marked inverse relationship with foetal age; in early foetuses, less than 25 mm, cardiac malformations were present in 68%. A wide variety of morphological abnormalities was encountered; these are listed. No cardiac malformations occurred in 72 threatened abortions which went to full-term delivery.