I’m getting a pacemaker tomorrow. What happens next as far as my Army career?

If it's a temporary pacemaker then it's a matter of whatever the underlying condition is and if the temporary pacemaker resolves it. Cardiac issues are a serious no go for continued service though. If it's a permanent pacemaker, at your age and time in service, you will be medically separated. Probably even medically retired

SPC (Join to see) do not forget to have a discussion with your personnel officer who will certainly have regulations to refer and explain the options to you. In the Navy they have something called "at the convenience of the government", when I had a medical change my duty station was extended one year. Then when reenlistment came up, there were duty station options and work assignments comparable to my skills. I would see if the Army had those options

I wish you luck brother and may god bless you.