The multiplication or reproduction of cardiac muscle myoblasts, resulting in the expansion of a cardiac muscle myoblast cell population. A cardiac myoblast is a precursor cell that has been committed to a cardiac muscle cell fate but retains the ability to divide and proliferate throughout life. [ http://www.ncbi.nlm.nih.gov/pubmed/26512644 GOC:rph GOC:BHF GOC:BHF_miRNA ]