Cardiovascular diseases, including myocardial infarction, are the cause of significant morbidity and mortality globally. Tissue engineering is a key emerging treatment method for supporting and repairing the cardiac scar tissue caused by myocardial infarction. Creating cell supportive scaffolds that can be directly implanted on a myocardial infarct is an attractive solution. Hydrogels made of collagen are highly biocompatible materials that can be molded into a range of shapes suitable for cardiac patch applications. The addition of mechanically reinforcing materials, carbon nanotubes, at subtoxic levels allows for the collagen hydrogels to be strengthened, up to a toughness of 30 J m^-1 and a two to threefold improvement in Youngs' modulus, thus improving their viability as cardiac patch materials. The addition of carbon nanotubes is shown to be both nontoxic to stem cells, and when using single-walled carbon nanotubes, supportive of live, beating cardiac cells, providing a pathway for the further development of a cardiac patch.