How can one respond to someone who says that the seat of the intellect is the heart, given the evidence that the brain is the source of decision-making, and taking into consideration heart transplant operations, and how is the Almighty's saying interpreted: "For indeed, it is not eyes that are blinded, but blinded are the hearts which are within the breasts"?

The seat of the intellect is the heart, and it has a connection to the brain. The origin of thought and contemplation is in the brain, and the origin of will is in the heart, as mentioned by Sheikh al-Islam Ibn Taymiyyah. The brain is like a secretary that organizes and arranges transactions and then sends them to the heart. Then the heart commands either execution or prevention. This is consistent with the saying of the Prophet, peace and blessings be upon him: "Indeed, in the body there is a piece of flesh; if it is sound, the whole body is sound, and if it is corrupt, the whole body is corrupt."