http://kidshealth.org/kid/htbw/heart.html
The positive points about this blog is that it has lots of sites that you can go on to do interactions.
The negative parts are it is more textbook than interactive. In the text it has wording for younger students, but those students will need to read well to understand the full web site. This web site has different areas to explore further areas to keep the student interacting. The only draw back would be that the students would possibly not want to search any further on the subject, it tries to cover a wide range of ideas all by itself. It even has places to look for recipies.

http://www.teachersdomain.org/resource/tdc02.sci.life.stru.circulator/
I liked this web site. It would be a great clip to use for any of the secondary classes that I would teach. I also like that it links to the curriculum content that is recommended from possibly the district that you are working in. It is definitely teacher based. This site uses deep thinking, because you are not just reading text, and the heart is beating in the video clip. This is just a tid bit of information catching the students attention, so they will hopefully want to explore different web sites, and follow up with what really excites them. It also gives background knowledge for the teacher who chooses not to do enough research on their own to find the important facts on the circular system. I would research more web sites for the students to look at, and then give them some options to explore. Possibly there would not be enough exchanges of thought that would take place, especially if the web sites were already published.