Complex sentence: Since they have such a huge metabolism, (their heart beats 600 times a minute), it's the busiest predator in the world and some species need to eat three times their own body weight in one day to survive.
Split into simpler sentences: Since they have such a huge metabolism, (their heart beats 600 times a minute), it's the busiest predator in the world. Some species need to eat three times their own body weight in one day to survive.