For checking the function of the sinus node or in patients with suspected pathological sinus node syndrome, a cardioplegic test is performed to check the intrinsic heart rate. The principle is to measure the frequency of impulses generated by the sinus node after completely blocking the innervation of the heart by the autonomic nervous system with a drug. This is done by administering a dose of 0.2mg per kg of body weight of atropine, followed 10 minutes later by a dose of 0.04mg per kg of body weight of atropine, and then checking the heart rate. The predicted value of intrinsic heart rate was then calculated with reference to the following formula, which equals 118.1 – age x 0.57 to give a value. In patients with sick sinus node syndrome, the intrinsic heart rate is lower than normal.