The primary culture of neonatal mice cardiomyocyte model enables researchers to study and understand the morphological, biochemical, and electrophysiological characteristics of the heart, besides being a valuable tool for pharmacological and toxicological studies. Because cardiomyocytes do not proliferate after birth, primary myocardial culture is recalcitrant. The present study describes an improved method for rapid isolation of cardiomyocytes from neonatal mice, as well as the maintenance and propagation of such cultures for the long term. Immunocytochemical and gene expression data also confirmed the presence of several cardiac markers in the beating cells during the long-term culture condition used in this protocol. The whole culture process can be effectively shortened by reducing the enzyme digestion period and the cardiomyocyte enrichment step. © 2008 The Society for In Vitro Biology.