Early clinical trials found that some women had congestive heart failure after they took Herceptin together with a type of chemotherapy called Adriamycin (chemical name: doxorubicin). In congestive heart failure, the heart muscle weakens and is less able to effectively pump blood throughout the body. When Herceptin is given without Adriamycin, heart failure is rare, mild, and usually treated successfully. Herceptin is commonly given with other types of chemotherapy, without an added significant risk of heart problems. In addition, many women take Herceptin alone with a very low risk to the heart.
Bear in mind that breast cancer with abnormal HER2/neu genes tends to be aggressive. So, for women in this situation, the benefits of Herceptin may far outweigh the risks.