Here's a little song i wrote (please enjoy it note for note) to explain it for you.
[to the tune of captain planet]
Blood!
Bullets!
Pain!
Sasha!
Hearts!
Go Heavy!!!
When my medic is charged I am Captain Heavy!
Captain heavy, he's a hero. gonna take your hitpoints down to zero!
you are cowards, you can't hide, from his gun cause you will die.
Captain heavy, he's a hero. gonna take your hitpoints down to zero!
gonna help him with an UBER, kill guys who like the scout and sniper.
(You're a real jackass, Captain Heavy!)
We are team RED, beating up team BLU.
'Cause kicking their ass is so fun to do!
booting Captain Heavy is not the way.
hear what captain heavy has to say.
"CRY SOME MORE!!!!"