The prevalence, range, and associations of congenital heart disease (CHD) were studied among 400 spontaneous abortuses between 9 and 40 weeks' gestation. Fifty-two (13.0%) cases of CHD were detected. To minimize selection bias the specimens were grouped by external appearance and the prevalence expressed accordingly. CHD was detected in 21 (7.3%) of 289 externally normal and 31 (27.9%) of 111 externally abnormal fetuses. Ventricular septal defect (VSD) was the most frequent CHD found in isolation as well as in combination with extracardiac malformations. Seventy-five percent of isolated CHD was VSD. Forty (69.2%) of the 52 cases of CHD were associated with extracardiac malformations. Chromosomal syndromes were responsible for a minimum of 19.2% of the cases and suspected in up to 36.5%. The most frequent associations involved the musculoskeletal system, central nervous system, abdominal wall, and kidneys. In contrast, studies of liveborn infants have reported 70% of CHD as isolated defects, including many CHD infrequently seen among spontaneous abortuses. This suggests that fetuses with isolated CHD often survive to term, and CHD does not significantly affect the survival of the fetus in utero. Ventricular septum formation may be particularly susceptible to hemodynamic changes and may be indicative of an underlying pathologic condition that also leads to a spontaneous abortion.