Is there a certain molecule that causes it or is there something in the molecular structure that causes it?

We have a project for general chemistry class wherein we have to modify an existing drug to remove a side-effect. We don't actually need to CREATE a drug; it's just a proposal that doesn't need to be very in depth. I'm actually a computer science student, so I'm not even sure about half of what I've read. I've asked a newly licensed pharmacist about what drugs can be possibly used with rosiglitazone to reduce the risk of heart failure, and she suggested istaroxime. Our professor is aware that we cannot master molecular modification in 2 weeks; we just have to explain why we want to combine the "something" in istaroxime to "improve" rosiglitazone.
If this is not possible, are there any other drugs that you can suggest that we can modify and doesn't require much in-depth knowledge in pharmacy so even non-medicine students can understand them? Thank you very much!