I'm sorry to hear you had such difficulty. Congrats on your 2 new buttercups, your going to have so much fun with them! (i'll bet you have already)
Ask your doctor if these exercises are safe for you.
If it's your abs you want to get in shape with out raising your heart rate to much, try these one at a time slow, casual, leg lifts.
(can be done while watching t.v. or reading)
Lay on your back, like this-
Bring one leg/knee, at a time, up to your chest, then straighten out/extend completely (leg level with horizon), then back to original bent position, foot on floor, repeat with other leg. You can do this on 3 separate occasions during the day, everyday, (positive results will soon follow.)
Do each repetition
slowly, this will keep your heart rate low. Start off with 10 reps for each leg, and see how you feel, perhaps keep a watch with a second hand available so you can check your heart rate.
Checking heart rate or bpm, beats per minute.
Count the number of beats in 15 seconds, then times that by 4, and there you will have your heart rate. Ask your doctor about maximum heart rate for your condition.