The words he'd, heed sound the same but have different meanings and spellings. Why do he'd, heed sound the same even though they are completely different words?
The answer is simple: he'd, heed are homophones of the English language.
Contraction of he had.
Contraction of he would.
To pay attention to; listen to and consider: "He did not heed my gibes, and chattered on” ( Sean O'Faolain).
To pay attention.
Close attention; notice.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").