Background: The neurohypophyseal hormones oxytocin (OT) and [Arg 8 ]-vasopressin (AVP) have recently been implicated in cardiac function. This study was designed to investigate actions of OT and AVP on regulation of the voltage-gated Ca 2þ channel in cardiomyocytes.Methods and Results: Cultured neonatal rat cardiomyocytes were stimulated with OT or AVP (10 À8 M to 10 À6 M) for 24-72 h, followed by real-time PCR and patch clamp studies. Although OT did not exert any modulatory effect on L-type Ca 2þ channel current, as a shortterm effect, stimulation of cardiomyocytes with OT but not AVP decreased the expression of Ca V 1.2 mRNA with a reduced L-type Ca 2þ channel current. A transcription factor CREB mRNA expression was down-regulated by OT treatment, although T-type Ca 2þ channels (Ca V 3.1, Ca V 3.2) were unaffected by OT or AVP.Conclusion: OT but not AVP down-regulates L-type Ca 2þ channel expression through the inhibition of CREB transcriptional, suggesting a novel mechanism of OT action in the cardiac electrophysiology. (J Arrhythmia 2010; 26: 111-118)