The heart is the symbol for being a fan.If the heart you see in a FanPage's profile has blue borders but is white in the middle, the user (a fan or another FanPage) isn't yet a fan of that FanPage. You become a fan by clicking on the empty heart: it then turns blue, and the user becomes a fan.
Being a fan of a FanPage means that the latest update that the FanPage has posted will be shown in your profile, both in the public profile as well as in your private view. That way whenever you log in to TeamUp you will easily see at one glance what your favorite FanPages are up to in your own profile, without having to visit each of the FanPages' profiles separately.
Users who have a business profile in TeamUp cannot become fans of FanPages by clicking on the hear symbol (because a business cannot be a fan of a FanPage). However, when a business has formed a partnership with a FanPage, the heart they see in that FanPage's profile is colored purple.
Business users also have the possibility of following a FanPage that they don't yet have a partnership with. That way they can see the FanPage's latest update in the private view of their business profile. This is an easy way to stay up to date with interesting FanPages that the business might be interested in forming a partnership with later on.
Read more:What does it mean when I become a fan of a FanPage? How do I become a fan?
How can I start following a FanPage?