Have you asked your medics?
You can accumulate exercise in chunks, it doesn't make any difference compared to long sessions So if you're happy with small chunks, continue, even 5 mins every so often will be helpful. Depends on your symptoms. A PT would use "rate of perceived exertion" for exercises & check you're comfortable.
See if you have any cardiac rehab PTs locally, they would be qualified to give you advice, may be one at the local hospital?
Do you feel safe on the bike? Think the worry would be falling off? Have you seen tricycles?
Basically, you're your own guru, talk to the doctors & then come up with a strategy that fits your own circumstances. Got to better than sitting but best to take advice. Good luck!
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