Cardiac auscultation of a 10-day-old diarrheic female Holstein dairy calf revealed irregularities in rhythm and absence of 4th heart sound. Electrocardiogram (ECG) and blood sample were obtained before and after the treatment. Based on ECG and cardiac auscultation findings, atrial fibrillation (AF) was diagnosed. Serum sodium, calcium and magnesium before treatment were significantly lower than their reference ranges and potassium was significantly higher. One day after treating this patient, serum electrolytes were reached to reference ranges and AF was changed to normal sinus rhythm. Based on resolving the AF after treating the patient and correcting the electrolyte imbalances, it can be suggested that electrolyte imbalances were the main cause of the occurrence of AF in the present case.