First, welcome on the Hive. There's plenty of variety of exercise here, and nice people, you will find your niche!
For your specific request...
No idea about exercise and diabetes, but other bees may have good suggestions to help maintain proper glycemia before and after workout.
For heart... First, speak to your cardiologist. There's a myriad of heart conditions - muscle, valves, irrigation of the heart itself... , each one with their own caveats and abilities, and he/she will know your exact cardiac "sufficiency" status and what you may do and what may be risky.
Personally, I was born with a cardiac malformation (aortic stenosis + mitral valve prolapse), had a first surgery as a young kid. But most importantly , as it decompensated, I had to have another open heart surgery in January 2020, and have a mechanical mitral valve now, + continued risk of atrial fibrilation. Between decompensation and surgery, it was ... no exercise. Zero. Even yoga had been forbidden. After surgery, I had rehab which helped immensely exercising again with trust. After rehab, I started "again" here using the easiest, level 1 programs, and daily walking ; and now have been able to progress to the level III workouts ; but this under the supervision of my cardiologist + my rythmologist.
So, in short, talk with your cardiologist, and then with authorisation progress litle by little! Exercising this muscle is part of rehab! Wishing you the very best.