TNNI3 and ventricular tachycardia: Horses with ventricular arrhythmias (ventricular premature contractions (VPCs) and/or ventricular tachycardia) and documentable myocardial toxicities or immunological reactions (n = 5) had cTnI concentrations of 0.09, 0.21, 0.31, 15.18, and >100 ng/mL (Table 1).