The term simplehearted, which means having a pure and sincere nature, is often used in a positive sense. However, there can be instances where one may need to convey its opposite meaning. Some antonyms for simplehearted are cunning, crafty, deceitful, sly, insincere, and treacherous. These words indicate an attitude of deceitfulness, dishonesty, and a lack of purity of heart which is completely contrary to the innocence and sincerity embodied by being simplehearted. Depending on the context and the intent, the use of the right antonym can convey the intended message effectively.