The fatter region of the penis, typically found towards the mid-shaft-section.
The worm heart bears its name from the bulge in an earth worm where the heart resides. It is a rare sight, but a real lethal weapon.
Bro: "Dude what's that fuckin' bulge?"
Me: "Don't worry about me bro. That's just my worm heart."
Me: "Dude Kelly was loving that worm heart last night"
Chris: "Damn man, I wish I had a worm heart"