Mexican heart taco is where you take a very large bore hypodermic syringe and inject human feces into one of the four main chambers of the human heart. When the victim wakes up and grabs their heart you have a huge lady sit on their mouth and poop until the victim suffocates. When the police come you pretend not to speak English.
NOTE -- often confused with a Mexican Crap Taco
Don't fall asleep, or Hans will give you a mexican heart taco.