The substrates for the reaction are
- heme
- three molecules of oxygen
- NADPH
The 
is a cleavage of the ring between the I and II pyrrole rings.
- The alpha-methylene group is released.
- The product is symmetric with respect to the propionic acid groups.
The products are
- biliverdin (pronounce)
- carbon monoxide (this is the only endogenous source of carbon monoxide)
- iron (II)
- NADP+
In the second 
biliverdin reductase reduces the central methene bridge of biliverdin, producing bilirubin.
Conversion of biliverdin to bilirubin requires NADPH as a reducing agent.