In a 4-year period, 83 fetuses have been noted to have an abnormal fetal heart position within the thorax on fetal echocardiography. In 55 cases where the heart lay in the right chest, this was due to the presence of a left-sided diaphragmatic hernia; in one case, the heart was abnormally far into the left chest because of a left-sided diaphragmatic hernia. Of the remaining 27 cases, the heart lay in the right chest in 16 cases. In seven of those 16, there was a congenital heart malformation; in six, there were lung anomalies; a hiatus hernia was present in one; both congenital heart disease and lung abnormality were present in one and one fetus had isolated dextrocardia. In nine cases, the heart lay in the center of the chest and in three, the heart lay further to the left than normal. Congenital heart disease was found in nine of these 12. Chromosomal anomalies were found in four of the 27 cases with an abnormal heart position but an intact diaphragm. In summary, it is important to be familiar with the normal cardiac orientation within the thorax and to investigate abnormalities of position. A diaphragmatic hernia will be the most common underlying cause but, where the diaphragm is intact, other explanations must be sought in order to counsel correctly or plan appropriate perinatal management. Lung disorders, congenital heart disease and chromosomal anomalies will be the principal differential diagnoses.