And Hashem said to Moshe Pharaoh s heart is kaved- heavy. Kaved also means liver. The Midrash says Pharaoh became angry based on a Gemorah in Berachos which says that kidneys advise, the heart understands, the tongue forms . Since the liver is the seat of anger, the Torah tells us Pharaoh s became kaved- angry. That certainly begs for explanation.
Man is composed of three systems.
The highest is knowledge, the middle is emotions and traits and then the lowest system, physical desires. Knowledge originates in the Mo ach- brain. Emotion stems from the Lev- heart. Desires are related to the Kaved- liver. When a person has his priorities set, his Mo ach at the helm, his Lev is on call and his Kaved is at bay.