Soul looked exactly like heart (anatomically correct heart, not "heart shape"), only it was on the right side of your body and it was transparent (not invisible).
That's how I imagined souls in Heaven/hell/purgatory too - hundreds of transparent heart muscles.
A childhood belief about general

others believed things like this
- The song called heart of glass mixed me up as a kid. I heard "Heart and ass". — oops
- I used to think that when people had heart attacks someone came and stabbed their heartAnon
- I used to think that if you eat pig heart, you could grow another heart and be twice as healthier. Anon
- I used to picture God as a giant transparent poodle after seeing "All dogs go to heaven".Anon
- I used to believe an artichoke was an animal and we only ate its heart. — Laura
- I used to believe that only people that were in love had a heart.— Nikki