The backhole of a heart is a large, valveless vein (aka the superior vena cava or SVC) that conveys deoxygenated blood from the upper half of the body and returns it to the right atrium. The SVC may experience a breakphase where the heart quiets down in order to expell any excess waste. This waste makes the back hole very slippery, thus making it perfect for heartanal.
"I feel like the back hole of my heart was about to burst last night... he was just so big..."
"..um, what is the back hole of a heart?"
"oh you poor thing.. you've been missing out! I can ask my friend, he'll show you. ehehe."
"uhh alright i guess?"