where is the film about this novel ?

The Heart of the Matter is a 1953 British film based on the book of the same name by Graham Greene. It was directed by George More O'Ferrall for London Films. It was entered into the 1953 Cannes Film Festival.[1] So, there is a movie but getting it can be tricky dependig where you are. There are various sites on-line mostly not quite legal. You can try NetFlix or a specialty video store if you live in a large city.

I couldn't find this movie for you even on netflix, but they do have copies at amazon for around $13.00- it's a great movie, hope you find it, but on the other hand............. read the book; it's really very good! :-)