COL3A1 and myocardial infarction: HSA+ CMs transcriptional profile resembles that of Cav3+ cells, although they express lower levels of transcripts for Gjc1, Arnt, Vim, Actnb, and Casq1 and, in contrast to their Cav3+ counterparts, do not express extracellular matrix transcripts, such as Col3a1. This population that likely corresponds to cells with a stochastic delayed maturation program persists, albeit at low frequencies, in the adult heart and responds to myocardial infarction (MI) by increasing in numbers.