I'm curious about what testing was done. I hope chest x-rays for the coughing at minimum was done. If the heart looked enlarged (due to heart failure), then an echocardiogram can pinpoint what is wrong specifically with the heart. Different medications can be used to manage various types of heart failure and help with the coughing, but it's concerning if they don't have a specific diagnosis on the heart condition. As far as the seizures, I'm guessing that they've done bloodwork to be able to rule out some metabolic issues, but that doesn't rule out a brain tumor...
I'm sorry to hear that you don't have answers yet. It's hard to know how to treat them if you don't know what's wrong.