All cats with cTnI > 0.16 ng/ml had significant echocardiographic or necropsy findings including left ventricular (LV) thrombus with relative systolic dysfunction, focal myocardial thickening (MT) and wall thinning (cTnI = 2.11), LV thrombus with MT (cTnI = 1.7), dilated cardiomyopathy (DCM) phenotype with congestive heart failure (CHF) (cTnI = 1.33), high grade second degree atrioventricular block with DCM phenotype and biventricular CHF (cTnI = 0.34), MT with severe left atrial (LA) dilation and DCM phenotype (cTnI = 0.23). This evidence concerns the gene TNNI3 and atrioventricular block.