TNNI3 and Ventricular arrhythmia: In the present study, all four cats fulfilled two major criteria (cTnI > 1.0 ng/mL and diagnosis of FIP), as well as between one and two minor criteria, including decreased left ventricular systolic function (cats 24 and 39), pericardial effusion (cat 39), ventricular arrhythmias (cat 40), and the heteroechogenicity of the myocardium (cats 38 and 40).