This study compared the sensitivity of ECG and cardiac troponins to predict cardiac histopathological changes, clinical severity, and survival in canine babesiosis. One control group (n = 9) and 4 groups of dogs with mild uncomplicated babesiosis (n = 8), severe uncomplicated babesiosis (n = 9), complicated babesiosis (n = 8), and babesiosis and concurrent immune-mediated he-molytic anemia (IMHA) (n = 9) were studied. A 1-minute lead II ECG was recorded, and cardiac troponin I (cTnl) and T (cTnT) concentrations in plasma were measured. cTnl concentrations were significantly higher in the complicated (mean, 9.9; SE, ±5.76) and concurrent IMHA (mean, 6.53; SE, ±4.32) groups and in the 3 dogs that died of the disease (mean, 22.17; SE, ±12.85) than in the control dogs (concentration below detection limit of test, —0.3 ng/mL). The 3 nonsurvivors had the most severe cardiac histopathological changes, but no arrhythmia and minimal other ECG changes. Dogs with babesiosis developed a variety of ECG abnormalities, but the abnormalities were not associated with disease severity, outcome, or plasma cardiac troponin concentrations. The exception was the presence of ventricular premature complexes (VPCs), which were associated with high cardiac troponin concentrations. This study showed an association between cTnl concentration and histological changes, clinical severity, and survival and no correlation between ECG abnormalities and histological changes or biochemical evidence of myocardial damage as reflected by cTnl concentrations. From this study, it was concluded that the analysis of plasma cTnl is a feasible and sensitive test and is superior to cTnT in diagnosing cardiac involvement in dogs with babesiosis.