Inflammatory bowel disease was linked to an increased risk for conduction defects and ventricular arrhythmia. It coincides with dysregulation of gut microbiota, increased inflammation, and deregulation of the renin-angiotensin system. In this study, we aimed to determine the mechanism of colitis-induced electrophysiological remodeling that increases the risk for ventricular arrhythmia. In a mouse model of dextran sulfate sodium induced active colitis (3.5 %, 7 days) cardiac electrophysiological properties were quantified during active inflammation. Electrocardiographic recordings exhibited a prolonged QT duration in mice with active colitis compared to control. Field potential (FP) recordings of Langendorff perfused colitis-hearts exhibited increased FP dispersion, a reduced threshold for ventricular alternans, and an increased propensity for spatially discordant alternans. The increased propensity for alternans was also reflected in isolated ventricular myocytes where Ca(2+) transient alternans occurred at lower pacing frequencies and increased alternans ratios. The action potential was unchanged during colitis but myocytes exhibited a prolonged Ca(2+) transient duration that corresponded with attenuated phospholamban phosphorylation. Stimulating cellular SERCA activity (Istaroxime), normalized the propensity for alternans. Serum levels of Angiotensin II (AngII) were increased during colitis and Angiotensin-converting enzyme (ACE) inhibitor or AngII receptor type 1 blocker prevented the increased alternans inducibility in isolated myocytes and hearts. Our data demonstrate that active colitis promotes reversible remodeling of ventricular Ca(2+) handling properties and increases the propensity for alternans and arrythmia. The changes can be prevented by ACE or AT1R inhibition supporting a cardiac benefit for controlling RAS signaling in patients with active colitis.