at heart vs to oneself

at heart

prep
  • In spirit; according to one's beliefs, views or feelings; deep down, fundamentally, really. 

  • Wished earnestly for; held in high esteem. 

to oneself

adj
  • Tending not to interact with others; introverted; reserved. 

How often have the words at heart and to oneself occurred in a corpus of books? (source: Google Ngram Viewer )