What should I expect after open heart surgery?

Hello @meredithd,
It looks like this is your first time posting...so an official welcome to Mayo Connect!
I read your comments and marveled at your inner strength and positive attitude, even though it sounds like you are having a tough time after surgery.
As a nurse, you probably already know that no two people are alike, so no two will have the same recovery. Three weeks is pretty new still, and it will take time for your body to recover from such an invasive surgery. Thankfully, it sounds like you were at the best place in the world for your complicated case. This is where they shine by taking on the most complicated cases.
I had a septal and papillary myectomy for HOCM at the Mayo, and had all the usual post-op conditions, but no real complications. I had atelectasis, which most everyone gets, so perhaps that combined with blood loss anemia is causing your SOB and fatigue?
You sound like you know your body, and that you listen to it. That's good because you will instinctively know when to stop and rest. You want to push yourself, but not over do it, if that makes sense.
I can share with you that I had terrible pain between my shoulder blades after surgery. Nothing helped, but in some instances I was able to position myself so it eased. I worked for a hospital remotely, and there was no way I could sit for 8 hours. Sitting, standing, walking, it just was so relentless. I ended up losing my job, even though I was still on a medical leave, as it took a year for that to go away. Every now and then when I am walking, it hurts. I don't want to scare you, just maybe give you information. I was told this was pretty common after open heart surgery because of the torque placed on your spine during your chest being cut and spread open. One thing that did help me, and maybe it will you too; I did some yoga before surgery and there was a pose called 'eagle arms'. At first I could barely cross one elbow over the other, but in time I was able to perform it, and boy did it help. You are only three weeks out, and you want to rest your sternum. I would wait and get your doctors advice for when you could start that.
Are you signed up for cardiac rehab?
There are some arm exercises they make you do that do help as well, like the bicycle pedals for your arms. It's gentle and a good start for using your arms. Again, you are really early in recovery and need to let the sternum heal. Typically, the usual magical six weeks. Like a fracture.
Coughing and sneezing definitely hurt in the recovery phase, so you are not being silly! Your sternum was cut open, wired back together, and it needs time to heal.
A month sounds pretty quick to go back to work in my mind, so my advice would be work with your doctor, and let them know if you feel you are ready. I too was released by Mayo to go back to work, but my hometown FP knew me and listened to me and kept writing me off for three months at a time until I was ready. He waited for me to tell him. Unfortunately, my hospital let me go a month before my last medical leave date was up.
I know I went on and on a bit here, but is there anything else you want to ask?

Wow. You have much more information/experience than I do on heart surgery, problems, etc. However, the soreness was definitely a part of my recovery experience. It finally ceased. I don't recall how long it took, but it was a number of weeks. Cardiac rehab, although tough at the time, did help.