Get the value of each row in Gridview??

hi

I have Gridview binded to Persons database table

Persons
PersonId - GUID
Name nvarchar
Age  int

on  Person.aspx  it displays 20 persons.
On button click I want to get the "GUID" of each of the 20 persons and
add the text to an mail message class in the body of the email.

thank you