By Stephanie Stahl

PHILADELPHIA (CBS) — An emerging field called cardio-oncology is growing for cancer patients who develop heart disease because of treatment. Millions of breast cancer survivors have had their lives saved as a result of early detection and treatment, but those therapies can be harmful.

Heart disease is the No. 1 cause of death among breast cancer survivors. Now, cardiologists and oncologists are working together to reverse that trend.

Four months into her fight against Stage 2 breast cancer, Andrea Cianfrani learned that she had a new health challenge to conquer.

After recovering from a mastectomy, Cianfrani received chemotherapy to attack her breast cancer, not knowing that it was also attacking her heart.

“It was a little bit of a surprise because I wasn’t feeling anything,” Cianfrani said.

An echocardiogram revealed the 40-year-old was in heart failure and was among the tens of thousands of breast cancer patients who develop heart disease each year.

Doctors prescribed medication to protect Cianfrani’s heart so she would be strong enough to finish chemotherapy.

“Cardio-oncology is a field that is growing. We’re all working very well together to take care of our patients, not only to improve their cancer outcomes as they survive but to improve their cardiovascular outcomes as they age,” oncologist Dr. Chau Dang said.

Breast cancer treatment puts the heart at risk in several ways.

Chemotherapy can damage the heart muscle that pumps blood, leading to heart failure and radiation can disrupt normal heart rhythm and damage both the lining around the heart and the heart valves.

But the biggest risk from radiation is the development of early and accelerated coronary artery disease, which raises the risk of a heart attack.

While some women have no symptoms, others experience shortness of breath, chest pain or decreased ability to exercise.

“The treatments are effective, the oncologists have determined that they work well, but now the issue is how we give the drugs more safely,” Dr. Javid Moslehi said.

Three years after completing treatment, Cianfrani’s heart is strong again, but she’ll be monitored for any lingering effects of the chemotherapy for the rest of her life.

Doctors say cancer treatments can be tailored to some degree to help reduce the risk of damaging the heart.

Stephanie Stahl