The heart is a metonym for what a person feels and desires and "the mind" is a metonym for what a person thinks and decides. Alternate translation: "a person's feelings and thoughts" (See: [[rc://en/ta/man/jit/figs-metonymy]])
The word "vengeance" here can be expressed as a verb. Alternate translation: "I will watch you take revenge" (See: [[rc://en/ta/man/jit/figs-abstractnouns]])