One hundred unselected pregnant women underwent M mode and two-dimensional fetal echocardiographic studies between 14 and 43 weeks' gestation. The following cross-sectional views were obtained: high parasternal short axis, parasternal long axis, four chamber view, and an extended long axis to assess the aorta. These views successfully identified great vessel orientation and size (90%), atrial and ventricular size and function (90%), presence of atrioventricular valves (92%) and semilunar valves (75%), and presence and continuity of ventricular and atrial septa (91%) and the aortic arch (68%). Factors that limited visualization were persistent unfavorable lie, maternal obesity, and oligohydramnios. Disturbances in cardiac rhythm were the prevalent abnormal findings (16%). In addition, several anatomic defects were detected in utero and confirmed at autopsy. These included a biventricular cardiomyopathy, atrial septal defect, pericardial effusion, and hypoplastic heart. The potential applications of our ability to detail human fetal cardiac anatomy and dimensions are discussed.