Phonosemantic compound. 心 represents the meaning and 原 represents the sound. In simplified Chinese 愿 is also used to mean "hope; wish", while in traditional Chinese this meaning is written with a separate character 願.

Evolution

Seal script

Shuowen (~100 AD)

Clerical script

Western Han dynasty (202 BC-9 AD)

Clerical script

Western Han dynasty (202 BC-9 AD)

Seal script

Western Han dynasty (202 BC-9 AD)

Regular script

Modern