The ability to express recombinant genes in cardiac myocytes in vivo holds promise for the treatment of a number of inherited and acquired diseases of the cardiovascular system. Several groups have demonstrated recently that plasmid DNA is taken up and expressed in cardiac myocytes following injection into the left ventricular wall in vivo. Recombinant genes introduced into cardiac myocytes by this technique are expressed for at least 6 months after injection, and appear to be regulated normally by humoral signals. In addition to its potential for somatic gene therapy, this method should prove useful for studies of transcriptional regulation in the heart.