BACKGROUND Fetal echocardiography is usually done during the second trimester of pregnancy, but waiting until that time can lead to anxiety for the parents if the fetus is at high risk of having cardiac abnormalities. We report the feasibility of transabdominal first-trimester fetal echocardiography for early reassurance of normality or a prenatal diagnosis of a cardiac malformation. METHODS We did first-trimester fetal echocardiography and colour-flow mapping with a 5 MHz curvilinear transducer at 13 weeks' gestation (range 12-13+6 days) in 15 fetuses at risk of cardiac defects. The fetus was judged to be normal if the investigation showed normal visceral situs, four-chamber view, and two normally related great arteries of similar size. We did second-trimester scans and neonatal follow-up for the women who continued with their pregnancies; necropsy was done in two cases of pregnancy termination. RESULTS Ten fetuses had normal hearts at the time of the first scan, which was confirmed during second-trimester assessment. In one fetus, the four-chamber view was asymmetrical and a moderate-sized apical muscular ventricular septal defect (VSD) was diagnosed after birth. In another two fetuses we diagnosed small muscular VSD on the second-trimester scans. A complex cardiac malformation was correctly diagnosed in one fetus at 12 weeks of gestation. Thus, in 11 fetuses, the imaging was of sufficient quality to reassure the family or to diagnose an abnormality. In the other four fetuses, the investigation was judged to be incomplete, but no definite cardiac abnormality was identified. CONCLUSIONS Transabdominal fetal echocardiography in the first trimester of pregnancy is feasible. In most patients the resolution of images is sufficient to allow assessment of basic cardiac anatomy, when normal, or detection of complex malformations, when present.