Objective To study the mechanism of isoproterenol triggering arrhythmia through myocardial mi⁃tochondrial oxidative stress in mice. Methods An electrocardiogram was recorded before and after intraperitoneal in⁃jection of isoproterenol. Myocardial tissues were extracted from the mice to measure the changes in the levels of mito⁃chondrial respiratory chain complex I

adenosine triphosphate (ATP)

and reactive oxygen species (ROS). The cardi⁃ac action potential was measured by optical mapping. Results After isoproterenol injection

the mice had a signifi⁃cantly increased heart rate

significantly more frequent arrhythmia triggered by pacing

significantly decreased levels of ATP and mitochondrial respiratory chain complex I

a significantly increased ROS level

and a significantly short⁃ened cardiac action potential duration. Conclusion Isoproterenol induces oxidative stress in myocardial mitochon⁃dria to trigger arrhythmia.