Calcium is one of the most important elements of the body. Milk fever, downer’s cow syndrome and anorexia are due to hypocalcemia, on the other hand increased serum calcium induces cardiac disrrythmias. Ten 4-7 years old holstein cows were used. Body temprature, heart rate and ECG were taken. Then commercial 40% calcium solution (100 — 500 ml) were injected, I.V. After injections (as shown on the table), body tempreture, heartrate and ECG were taken. The standard lead was base — apex. Serum calcium rate with spectrophotometry was determines. After injection of calcium, duration of T an QRS waves were variable. R-R interval and QT segment were prolonged and shortened respectively. Firs degree A — V block and ventricular premature beats were also observed.