If it's a part of who you are, then I would absolutely include it. You should include all of your work experiences/hobbies on your application because the more things you list, the more well-rounded you will appear. However I would caution against mentioning finance as a "passion" because, as was said above, people will ask you why you are pursuing a career in healthcare instead. You should have a good reason for this question ("why medicine?") and if finance is a part of that (e.g. you want to puruse a joint MBA/M.D. degree), then that's even better!