This can happen some times in newborn babies due to delay in maturation of the conducting system of the heart which is responsible for the heart beats.
Electrolyte abnormalities like sodium, potassium, calcium in the blood also can cause changes in heart rate
However we have to wait and watch the baby.
Look for any abnarmal signs like breathing difficulty,blue colour of the lips,etc and if you find anything abnormal get back to the doctor.
All the best