Why heart transplant patients died because bacterial infections?

Question

many of this patients died not from the rejection of the transplanted heart but from bacterial infections.

Answer 1

As Andy has stated in the first answer immunosuppression is one reason.,  The other problem that these  drugs cause arteriosclerosis, to occur sometimes quickly, so they can die from a heart attack.

Answer 2

Because they receive immunosuppressants prior to surgery to reduce the risk of rejection. Thus, they are very susceptible to infection, as their immune system has been shut down. Antibiotics are frequently insufficient to combat the bacteria.