Abstract

The zebrafish (*Danio rerio*) serves as a critical model for understanding vertebrate cardiac function and disease. This study provides a comprehensive analysis of the **electrophysiology of the *Danio rerio* heart**, focusing on the underlying cellular and molecular mechanisms that govern cardiac excitability. Our primary objective was to characterize the action potential morphology and ion channel contributions in isolated ventricular cardiomyocytes. Using patch-clamp electrophysiology, we recorded and analyzed key membrane currents, including the inward rectifier potassium current ($I_{K1}$), the L-type calcium current ($I_{Ca,L}$), and the transient outward potassium current ($I_{to}$). The results reveal a distinct action potential profile in *D. rerio* cardiomyocytes, characterized by a relatively short duration and a prominent plateau phase, which is primarily sustained by a balance between $I_{Ca,L}$ influx and repolarizing potassium currents. Specifically, we demonstrate that the density and kinetics of $I_{Ca,L}$ are crucial determinants of the action potential duration, highlighting the central role of membrane ion channels in regulating cardiac rhythm. These findings establish a detailed electrophysiological baseline for the *D. rerio* heart, which is essential for future investigations into genetic cardiac channelopathies and the development of novel therapeutic strategies.