The regional paediatric cardiology centre in Northern Ireland has a telemedicine network linking the neonatal units of three district general hospitals using ISDN and IP-compliant equipment. We have previously reported the use of ISDN transmission at 128 kbit/s for remote echocardiography. In a series of 61 patients, a total of 59 transmitted scans were of sufficient diagnostic quality to confirm or exclude the presence of major congenital heart disease (CHD). There were three diagnostic errors (7%). Subsequently, we have examined the use of ISDN transmission at 384 kbit/s. Echocardiographic studies were carried out on 21 patients and all were followed up. Fourteen patients (67%) had CHD confirmed. There were two diagnostic errors (10%). Our experience of transmitting live echocardiographic images suggests that ISDN at 384 kbit/s provides the optimum balance between the clarity of the transmitted images and costs. We expect that IP videoconferencing will offer similar quality but at a lower running cost, and are currently assessing it in a pilot study. All sites within our network will remain capable of ISDN transmission until the efficacy and reliability of IP transmission has been demonstrated in a controlled trial. The clinical telemedicine service has led to the earlier diagnosis of and instigation of appropriate treatment for CHD.