This study was designed to evaluate serum and electrocardiographic (ECG) changes in cattle with foot-and-mouth disease (FMD). Thirty-two cows with clinical signs of FMD and 13 healthy cows were randomly enrolled. After blood sampling, ECG was performed on 23 of the 32 ill cows. Serum circulatory troponin I (cTnI), CPK, LDH, and CK-MB activities were determined in the patient and control groups. Arrhythmias including ventricular tachycardia (VT), sinus tachycardia (ST), atrial fibrillation (AF), and premature ventricular complex (PVC) were seen in 4, 4, 2, and 1 of the patients, respectively. The patients had higher cTnI levels than the control group (P = 0.05). A significant rise in cTnI was observed in patient cows with VT (0.86 ± 0.33; P < 0.01) and AF (0.22 ± 0.01 ng/mL; P < 0.05) in comparison with the control group (0.14 ± 0.04 ng/mL). The most significant finding of this study was the death of all of the cows with VT. It appears that the cause of death in the cows with VT was cardiac impairment, which was marked by serum cTnI elevation. It can be concluded that cows with VT have a grave prognosis. In some FMD cases with an increase in cTnI, AF was also observed, but with a fairly good prognosis.