Your frustration is appreciated and understood. Many people find themselves in difficult circumstances like this without knowing how to work through the problem. You may need some help finding the optimal approach to your back pain.
Having other mobility problems (e.g., ankle pain, knee or hip arthritis) can certainly put a monkey wrench in the solution. Other health concerns faced by many people are called comorbidities. Comorbidities include such things as the heart condition you mentioned. Other people say the same thing about their diabetes, cancer, high blood pressure, and so on.
Bu, in fact, study after study show these are the very problems for which exercise is best suited. Some experts go so far as to say, “Exercise is the most important drug in America.” What they mean is that when medications are stacked up against exercise for heart disease, exercise yields the best results most often.
The challenge you are facing is in finding the right kind of exercise — something you can tolerate while getting some benefits. A pool-therapy program may be helpful. Some folks respond well to exercise on a recumbent bike. The best person to help you with this may be a physical therapist.
Therapists are trained to assess strength, motion, and function and then find optimal ways to help you manage your symptoms. This often includes exercise but may start with heat or cold modalities to help reduce the pain and make it possible to move more.
At first, it may seem a bit like eating an elephant. But as the old saying goes, you do it one bite at a time. With painful musculoskeletal problems, time and persistence are required to find what works best for each individual. Take the first step, be patient, and keep working to find what combination of care helps you the most to get on (and stay on) the road to recovery. Good luck!