jpareyt,
Thanks for the post, and sorry to hear of your family's ordeal.
Unfortunately, chances are that the fast heart rate is an appropriate response to your Dad's illness. When we exercise, develop an infection, fever, are scared, or suffer large heart attacks; a natural response is tachycardia (fast heart rate). Slowing down the heart rate without correcting the underlying illness/affliction can be detrimental. Some of the worst mistakes I have seen are when well-meaning doctors slow down the heart rate without properly investigating why it was fast in the first place.
Make sure that a cardiologist, as well as the surgeon, is following your Dad's care. And consider moving him to a large center (if he is not at one) if you don't like what you see.
Best of luck.
It is not at all uncommon to have rapid heart rates after open heart surgery. For example, atrial fibrillation and atrial flutter are very common after surgery. These arrhythmias can be treated fairly easily with medications and if not successful with meds, an electrophysiologist will have other options. I had these arrhythmias before and after surgery. It is difficult to cope with the increase in rates but I am sure your Dad's medical team are doing everything possible to get it under control. The fact that he had a heart attack before surgery will complicate the picture somewhat.
They seem to be having trouble with the right medications. Any idea which ones helped you?