What was involved with Kelly's first chemo session and why would she be limited to only four doses of the anti-cancer drug, Adriamycin?

At her first chemo session, the first two bags of medication didn't seem bad. The first was saline and the next was anti-nausea medication. The third bag was the anti-cancer drug, Adriamycin. The nurse, Catherine, infused the cherry red medication manually, telling Kelly to let her know if it became too unbearable and she would slow up the infusion. Kelly learned that she would get only a total of four doses of this medication because it was very hard on the heart. Even if she got cancer in twenty years from then, she probably would not receive more of the drug. That's how powerful it was. Next she was given Cytoxan that was infused over the next several hours