Smallville :

A secret experiment that Lex is conducting at LuthorCorp goes terribly awry and causes the release of a dangerous toxin into the air. Smallville residents infected by the toxin, including Clark, Lana, Lex and Jason, imagine their greatest fears coming true and lapse into a coma.

Desperate to find a cure, Clark gives some of his blood to Lex and heats up the vials containing a cure while Lex is not looking. With the cure heated to the correct temperature Lex does something unexpected with the unproven antidote.