I need help in knowing which test to perform with this analysis.

I have two groups (lets say group A and B). A study was performed with initial rates of heart failures in group A and B (i.e, baseline rates) were measured. After 6 months of follow up the heart failure rates in group A and B (i.e, re measurement rates) were measured again.

By simple mathematics, I know that the improvement rate in better in group A as compared to group B.

I have to prove that the differences in rates in both groups are statistically significant.

I am using t-test for this but not sure how to go about it.

I would appreciate your suggestions.

Thanks a lot.