Cachorro literally means "puppy" or "dog". While it's a common word, its use in the song title "Coração Cachorro" (Dog Heart) is particularly interesting and memorable.
In this context, it's used metaphorically to describe a heart that is wild, untamed, and perhaps a bit foolish in love, much like a playful and impulsive puppy. The song personifies the heart as a dog that
This piseiro hit from Avine Vinny and Matheus Fernandes plays on a simple idea: a "dog heart" is a heart that can't help chasing after someone, even when it knows better.
The singer is finally starting to feel okay after a breakup. He accepts a night out for a drink, only for everything to fall apart the moment he looks over and sees his ex at another table with someone new. That's when his "dog heart" takes over: the same restless, barking heart that still loves her and can't stop reacting the second it spots her.
The chorus leans into that image with playful "Aú" (woof) sounds, turning heartbreak into something closer to a joke than a tragedy. It's a lighthearted, danceable way of admitting you're still hung up on someone.