A newborn girl presented with asphyxia, joint contractures and diminished spontaneous movements. Echocardiography showed hypoplastic left heart. Spinal muscular atrophy type I (SMA I) was diagnosed by detecting a homozygous deletion in the survival motor neuron 1 gene (SMN1). In the first trimester of a subsequent pregnancy, SMA I, hypoplastic left heart, and contractures were identified again. Congenital heart defects (CHD) have now been reported in 20 patients with SMA I, including three previously reported siblings and our two siblings, leading us to hypothesize that SMA I/CHD represents a unique phenotype of SMA I rather than a coincidental association. The homozygous SMN1 deletion may play a role in the development of CHD when it occurs in the presence of mutations or polymorphisms in other genes important for cardiac development. © 2008 Wiley-Liss, Inc.