^^^
I assume (always dangerous, I know) that a triple bypass, like the valve surgery I underwent, involves splitting the sternum. Now that you're home, it's held together with stainless steel baling wire (essentially). My surgeon explained to me that it takes a LONG time for the bone to graft together. That's why the restriction on lifting weight, and that's why they don't want you to drive. My surgeon imposed both the weight restriction and the no driving restriction for eight weeks after I was released.
He didn't mention shooting and I didn't ask, because I don't want any mention of GUNZ!! to show up in my medical records. I just decided if I wasn't allowed to even sit behind a steering wheel, I probably shouldn't be shooting -- especially not rifles, which bear directly on the shoulder adjacent to the chest and ribs. By the end of the eight weeks with such restrictions, I had lost a lot of muscle tone and I needed cardiac rehab to get back to some semblance of normal. When you do get back to shooting, you're going to want to start with something small and light, like .22, because your muscles won't be capable of shooting even half decently with heavier stuff.