If you have heart disease and have had a heart attack, even one of the 'silent' kind, it means your heart has been injured. It's like trying to lift a weight with a torn muscle - you just damage it worse. But with the heart, this will kill you instead of just hurting incredibly. You can still do quite a bit to help your heart recover, but doctors are extremely conservative about the kind of thing they want you to do, and most of them will be terrified that you will kill yourself by over-reaching. Very few cardiologists are also experts on the effects of exercise and how to do it safely. The problem is, if you never exercise your heart, it won't be stimulated to get stronger, and your cardiovascular system will just clog up some more.
The answer is to tell your doctor you want to do exercises and make diet changes that will help you recover. You may have to do research, you may have to find a doctor who has worked on exercise as a component in cardiac recovery.
If this method were to be useful for you, you would need to do it in a place where you have immediate medical care available in case you over-do it. You would need to have a heart rate monitor on. You may not want to do it with a bicycle - walking on a treadmill would do the same thing. Your maximum heart rate would be 70, so you would not want to go above 63, until your doctor says it's safe. You would also want to be careful, and take it slow.
For a person who hasn't injured their heart, but is just in lousy shape, this method will help them get in better shape. For a person who is in good shape, this will help them get in better shape.
It trains the ability to go to a peak effort, sustain it for a short time, then recover. This is the kind of fitness needed to escape a predator, to fight off an enemy, to catch prey, to haul a heavy object.
This is the same kind of pattern that coaches were inflicting on high school and college students in the 1970s-1980s as "wind sprint fitness drill" -- and everyone hated it then too.