In an attempt to become valedictorian of my high school, I was advised by my counselor to take an art history course over the summer through a local public charter school. The reason behind this decision is because my school does not offer any AP/IB (weighted) visual performing arts class that will fulfill the UC A-G requirements/my high school’s graduation requirements. I am going for a 5.0 for both my junior and senior years. However, I am now hearing that even though I am taking the art history course over the summer, it will still affect my GPA. Is this true and does anyone have any experience with summer courses. Thank you for your time 
you need to ask your HS counselor. we have no idea how you HS handles summer classes taken at other schools. .
If you are applying for the UC’s, summer courses that are required to meet the a-g courses will be included on your HS transcript starting with the summer before 10th grade through the summer before 12th grade. If they were not included, then you would not get credit and your application would be missing the (f) requirement.
@Gumbymom Will they be included when calculating my GPA?
The answer to the question varies by school. Since your GC suggested, presumably, in your case, it does. However, ask your GC to be sure; none of us are familiar with the policies of your school.
As @skieurope stated, it will depend upon your school, but if it is a required class for the UC’s then it would be calculated into your UC GPA. http://rogerhub.com/gpa-calculator-uc/