With triple bypass surgery doctors usually use a blood vessel from the leg for "spare parts".
Another option is a healthy mammary blood vessel. Nursing may strengthen and enhance mammary blood vessels making them useful as "spare body parts' many years later. In bypass surgery, the mammary vessel has a life expectancy of ten-plus years while a leg vessel has a life expectancy of five-plus years.
Wow. New use for the "girlies" after the hard work is done.
source: The Gem Sunshine LLL area newsletter