Why do squids need to have three separate hearts?

Since this is not my area of expertise, I searched Google under the key words "Squid anatomy hearts" to get these possible sources:

http://www.thewildones.org/Curric/squid.html
http://en.wikipedia.org/wiki/Squid
http://72.14.253.104/search?q=cache:nU60VQAr2pQJ:www.aqua.org/downloads/pdf/Outreach_Squid_Lab_Teacher_Booklet_Sept_2005.pdf+Squid+anatomy+hearts&hl=en&ct=clnk&cd=7&gl=us&client=safari

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search.

I hope this helps. Thanks for asking.