ALWAYS consult with your surgeon before applying ice packs OR heat packs to your surgical site. And BE CAREFUL with companies that advertise these products for use in the immediate post-op period.
The concern with ice: Following your mastectomy one of the biggest concerns is the quality of blood flow that remains to the skin. When ice is introduced, the remaining blood vessels in the skin shrink, further limiting the already fragile amount of blood flow that is providing oxygen and nutrients to the surgical area. This can lead to higher incidence of skin necrosis (skin death) and cause a completely avoidable surgical complication.
The concern with heat: During the mastectomy, all of your sensory nerves to the skin are damaged. This results in a numb (or mostly numb) sensation to the skin of the chest. If we apply heat to skin that has decreased or no sensation we are unable to feel when the temperature of the heat pack is getting too hot. Burns and other serious damage to the area can occur, once again causing a completely avoidable surgical complication.
There can sometimes be a role for both of these therapies in later stages of recovery, but always check with your surgeon for clearance to use ice and heat therapy first.