Irreversible congenital heart block (CHB) and the transient rash of neonatal lupus are strongly associated with maternal antibodies to SSA/Ro and SSB/La proteins; however, the precise mechanism by which these antibodies mediate organ-specific injury is not yet defined. Culturing of keratinocytes has provided critical insights. Accordingly, successful culturing of human fetal cardiac myocytes at high yield would constitute a powerful tool to directly examine conditions that promote expression of the target autoantigens. To accomplish this aim, fetal cardiac myocytes from 18- to 22-wk abortuses were established in culture using a novel technique in which cells were isolated after perfusion of the aorta with collagenase in a Langendorff apparatus. After preplating to decrease fibroblast contamination, cardiocytes were grown in flasks and slide chambers. Staining with monoclonal anti-sarcomeric alpha-actinin revealed the expected striations typical of cardiac myocytes in 70-90% of the cells after 4 d in culture. Furthermore, the cells were observed to beat at rates varying between 25-75 beats per minute (bpm) after the addition of 1.8 mM CaCl2. An average yield of 45-60 x 10(6) cells was obtained from a 3- to 5-g heart. Cellular localization of SSA/Ro and SSB/La by indirect immunofluorescence and demonstration of mRNA expression by reverse transcriptase polymerase chain reaction supports the feasibility of cultured cardiac myocytes for the study of congenital heart block. In contrast to the increased expression of SSA/Ro reported for keratinocytes, incubation of cultured human cardiac myocytes with either 17beta-estradiol or progesterone did not alter mRNA expression or cellular localization of 48 kD SSB/La, 52 kD SSA/Ro, or 60 kD SSA/Ro. In summary, we describe a novel method to successfully culture human fetal cardiac myocytes that should provide a valuable resource for investigation of the molecular mechanism(s) contributing to the development of congenital heart block. Differential constitutive and estradiol-induced expression of 52 and 60 kD SSA/Ro in human cardiac myocytes compared with keratinocytes may be a factor contributing to the marked discordance of clinically detectable injury in these two target tissues.