Unguarded tricuspid valvar orifice in the fetus.

The unguarded tricuspid valve is uncommon. We describe herein a fetus with a grossly dilated right ventricle and atrium, with severe tricuspid and pulmonary valvar regurgitation. The right ventricle was akinetic, and no tricuspid tissue or valvar apparatus was identified. Colour Doppler showed a highly unusual retrograde flow of blood through the right heart. The pregnancy was terminated, and necropsy examination confirmed the gross dilation of the right heart chambers, with severely dysplastic valvar tissue at the right atrioventricular junction effectively giving an unguarded orifice. There was no valvar displacement, and the left heart was normal. The fetus had a normal karyotype, albeit with absent kidneys.