Among the frequently reference genes used in cardiac muscle, we can mentioned beta actin and GAPDH (glyceraldehyde-3-phosphate deshydrogenase). Both genes appears frequently used as controls because of their respective muscular specific expression and their large and stable expression in cardiac cells. Howerver as Mrs Gund says, all depend of the type of your experiment, in particular what you want to demonstrate whether in normal or pathological conditions.
I would advise you to run a preliminary qPCR experiment to test a number of potential references genes (usually 8) against a random but representative selection of your samples (usually 12). The Cq values can then be analysed using a variety of programs such as GeNorm or NormFinder to identify the best reference gene or combinations of genes for your study as described in the following http://genomebiology.com/2002/3/7/research/0034/