First of all, I agree with the above posters that you should take your PS down and just PM it to people.
Second, I think you really need to go over linking clauses in sentences, especially comma and conjunction usage in compound sentences.
I also think that you've got a transitioning problem, which is most evident from the first paragraph to the second paragraph. Work on writing transition sentences at the beginning of paragraphs to link your paragraphs together in a cohesive personal statement.
Also, your first paragraph makes it sound like the heart that you looked at in high school was still beating and not full of formaldehyde with veins and arteries dyed bright colors for explanation purposes. Unless you went to a really fancy pants high school, you might want to reword that paragraph.