The aim of this study was to investigate whether in vitro differentiation of human bone-marrow (BM) and cord blood (CB) derived CD133+ cells would trigger the expression of cardiac proteins. BM and CB derived CD133+ cells were immunomagnetically isolated and cultured for 4 days in fibronectin-coated chamber slides in DMEM media containing: FBS, endothelial cell growth supplement, retinoic acid, dexamethasone, prostaglandin-E2, interleukin-2, fibroblast growth factor 4 and bone morphogenic protein 4. The cells were assessed for haemopoietic marker CD133 and the cardiac markers troponin I and actinin. Following isolation, a purity of 82% and 92.8% was achieved for BM and CB derived cells respectively. Immunophenotyping prior to culture demonstrated the expression of CD133+ marker (71% and 79% for BM and CB derived cells respectively) and undetectable expression of cardiac markers. Immunophenotyping after culture demonstrated reduced expression of the CD133+ marker, while 11.6% of CB and 6.2% of BM derived CD133+ cells expressed the cardiac protein troponin I (p<0.05). Furthermore, 5.1% of CB and 2.3% of BM derived cells expressed the cardiac protein actinin (NS). In conclusion, selected human adult BM and umbilical CB derived CD133+ cells express cardiac proteins following in vitro differentiation in an appropriate medium.