RGS5 and Myocardial fibrosis: The major findings are as follows: (1) Rgs5–/– prolonged ventricular repolarization and increased spatial heterogeneity of repolarization; (2) Rgs5–/– steepened APD restitution curves and increased spatial dispersion among ventricle; (3) ventricular tachyarrhythmia was facilitated by Rgs5–/–; and (4) Rgs5–/– induced VA, which was not dependent on myocardial fibrosis.