Real-time three dimensional echocardiography is increasingly used for imaging patients with congenital cardiac malformations. One of the limitations of a transthoracic approach is that intervening structures can impact on the quality of the images obtained. We hypothesised that, during surgery, epicardial three-dimensional echocardiography would provide images of high quality. We report our findings in eight children or young adults, with weights ranging from 2.8 to 70 kilograms, in whom we used this approach. In all cases, we obtained images of good quality, which could be analysed rapidly in the operating room. Of the eight cases, seven had echocardiographic findings which matched exactly the surgical findings. The remaining child had been diagnosed echocardiographically with a cleft in the aortic leaflet of the mitral valve, but was found at surgery to have a double orifice in the valve.