What is the meaning of 心兴? What is the meaning of 心兴 in the picture below (towards bottom left in image)? I am guessing it means to think, but doesn't 想 mean to think?
That character is not「兴」(to rise > excited, happy), it is「头」(head).

「心头」(literally heart + head) means mind - the picture is saying that you use your mind to think/reason.