Hi, Student,
I have two Bachelors Degrees and a Masters Degree, but not in medicine.
Here is a site listing the most common 6 courses required for entrance into Medical Schools:
http://www.studentdoc.com/medical-sc...uirements.html
No, you don't need a Bachelors Degree in the same field as a Masters Degree; but it does depend on the Masters Degree prerequisite courses, and as a rule-of-thumb, are normally found in the course content for a Bachelors Degree, leading up to a Masters in the same field.
The MCAT results are VERY important. Check with the Med School you are considering, or call them, and they will mail you a listing of their required prerequisite courses for entrance. Also, check with the college counselors. They have information on different schools.
If you would like to email a school, asking about the prerequisites for admission, here is a link to the prestigious Mount Sinai School of Medicine (New York):
http://www.mssm.edu/bulletin/admissions/admissions.htm