Q:

真心 VS 认真 difference

I was trying to say “He made this with all his heart” and then looked for how to say “with all one’s heart” in Chinese.  I found a lot of ways to express the sentence but I’m still not sure which one would be the most suitable because there were a lot of words and idioms that appeared: 

真心，认真，诚心，全心全意，真心实意. 

I’m not sure if native speakers often use those idioms, therefore I’m going to kick both idioms (全心全意 and 真心实意) out of the list, leaving the rest: 真心，认真，and 诚心. 
However, 诚心 comes as a noun in the dictionary (even though it also comes as an adjective, but the first word class of 诚心 that appeared was noun and I didn’t see any sentence that used it as an adverb).  Leaving only 真心 and 认真.  I’m not sure the difference between both words though.  Could someone please explain it to me? 

A:

真心 is sincerity (usually in emotional / relationship kind of manner)， while 认真 is serious. 
我是真心的  I am sincere (about it)
我是认真的  I am serious (about it)

