Eat not the Heart
This is the 30th Symbol in the Protreptics of Iamblichus. Pythagoras forbade judges and priests to eat animal food at all, because it was taking away life. Other persons he did not wholly forbid this food, but he restricted them from eating the brain (the seat of wisdom) and the heart (the seat of life).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894