The echo a couple of months after surgery seems to be normal protocol. I had surgery at the end of February, then had an echo in early April. When I met with my cardio last week, he said that unless I run into problems, we won't need to do another echo until next April - a year after the post-op echo. For me, that's an improvement, as I've been on a schedule of echo's every 6 months for the last couple of years.
As for the Holter monitor, often cardio's will have you wear one for a while if there is something they see that is slightly amiss in your heart rhythm. I would think that if they saw anything serious or life-threatening, they would tell you to come in or go to the ER right away.
I know it is all hard on your nerves, but try to remember that your heart (and the rest of your body) has just been through a massive shock in surgery. It will take time (months) for all to settle down. The good thing is that for most of us (and probably you're in that "most") the big things settle down and let us get on with life while the smaller things get sorted out.
Stay with the program. Just do what they ask and see what develops - it will probably all work out smoothly.
