Writers who are searching the Internet for health information, perhaps for a character, symptom or scene -- here’s a place to get a good start: Healia.
It has a lot of information and is searchable. You can search the web, medical journals and even clinical trials. There are also Health Guides, so if your character has heart disease, you can find the basic information here and that will most likely give you a base on which to build more detailed information.
This site even has its own medical blog. You can follow the blog to get book ideas. Be sure to check the sidebar for other blogs related to medicine.
There are health communities where you can ask experts questions, but I wouldn’t do this unless you have already done extensive research on your own since this isn’t a site dedicated to curious writers, but to patients or people with medical problems or looking for support.
So, if you need to know about breast cancer or asthma or some other medical ailment for a character, here’s a place where you can start your research.
5 months ago