AbstractA preliminary experimental study in dogs was conducted to evaluate the feasibility of transvenous cardiac pacing in the fetus with complete heart block associated with hydrops. Four young mongrel dogs were anesthetized with intravenous administration of sodium pentobarbital and mechanically ventilated, and a pacing lead was inserted via the tricuspid valve. The right ventricular cardiac output, aortic pressure and central venous pressure were measured, and the tricuspid valve regurgitation was measured semi‐quantitatively using echo‐Doppler color flow imaging. The relationship between the location of the pacing lead and the tricuspid valve regurgitation and cardiac function was examined.The mean right ventricular cardiac output when the pacing lead was inserted into the superior vena cava (126 ± 54 mL/min per kg) was not significantly different from that when it was inserted into the right ventricle (110 ± 43 mL/min per kg). The aortic pressure was 66 ± 7.7 mmHg and 67 ± 6.6 mmHg, respectively, and the central venous pressure 5.9 ± 1.7 mmHg and 5.7 ± 1.6 mmHg, respectively, under the two conditions (not significantly different). The ratio of demonstrating significant tricuspid valve regurgitation was 4/13 into the superior vena cava and 5/13 into the right ventricle, respectively (not significantly different).The location of the pacing lead did not change the cardiac function or the amount of the tricuspid valve regurgitation in our experimental study. It was therefore concluded that the transvenous cardiac pacing technique has potential application in intrauterine transvenous cardiac pacing in the fetus with complete he