It depends on why you want to contact them. What are your motives?
Do you want to just be friends and if so what kind of friends.
The kind of friends that talk once a month and sometimes hang out together
Or the kind of friends that talk twice a year and only see each other once on hoildays
To catch up.
Or do you what to date them again.
What ever it is you have to make it clear to yourself in your mind and heart first
Before making contact. Then make it clear to the person your contacting.
Also they might have questions that you need to answer. I think so often when people
Break up there are so many unanswered questions. I also think that making contact
Could be a good thing so both people can really truly settle things. Its better to make
Contact after three or four years than waiting seven or eight years later when its too late.
But then I have read success storys of lovers who haven't seen each other in 15 years
Get back together and get married.

It all depends on the person and reason
Good luck
Go make contact