The aim of this study was to determine the serum potassium levels in dehydrated calves with diarrhea and was to make electrocardiographic examination of the heart. The study was performed on 10 calves with diarrhea and 5 healthy calves, 4-12 days old, brought into the Animal Hospital to University of Firat. The average potassium levels was determined in calves with moderate dehydration as 8.33 mEq/L, and in calves with mild dehydration as 6.3 mEq/L, respectivelly. The Electrocardiogram (ECG)results revealed the absence of P-waves and the the peak of the T-waves in hyperkalamic calves with moderate dehydration revealed, and reduded amplitude of the P-waves, the prolonged QRS complex and negative peak of the T-waves in moderately hyperkalemic calves with light dehydration. As a result, hyperkalemia may develop in calves with diarrhea in certain degree, this is clinically determined and may be introduced in the ECG examination. Taking preventive measures against hyperkalemia could be useful in planning treatment od diarrheic and dehydrate calves.