palpitations

I underwent bypass surgery 3 years ago, I feel great, strong and also train well. My blood pressure is perfect a little low. But my pulse is twice as high at rest 70-75. In sleep he is 52, and most of the day does not go over 67. But before all the time I was on 55 and below. What can affect that? Is it anxiety? Or a heart defect as a result of the surgery?