Gender-related differences in cardiac function have been described in the literature, but whether the presence of sex hormones is responsible for these differences remains unclear. This study was designed to determine whether testosterone regulates the gene expression of calcium regulatory proteins in rat heart, thus playing a role in gender-related differences in cardiac performance. Ventricular myocytes were isolated from two-day-old rats and treated with testosterone at varying duration; the levels of gene expression for the androgen receptor (AR) and major calcium regulatory proteins were determined by quantitative real-time PCR. Testosterone (1 microM) treatment induced a maximum increase in beta1-adrenergic receptor and L-type calcium channel mRNA levels following an eight hour exposure. Six hours testosterone treatment stimulated a 300-fold increase in androgen receptor message abundance, and Na/Ca exchanger mRNA levels reached a maximum level following twenty-four hour testosterone treatment. Taken together, these data provide the first evidence that testosterone regulates gene expression of the major calcium regulatory proteins in isolated ventricular myocytes, and may thus play a role in the gender-related differences observed in cardiac performance.