Imagining one’s self without a heart can make it hard to draw breath. Without a heart, you’d have no blood pumping and you would start to die. This would make it increasingly harder to draw breath and get oxygen to stay alive.
You know how when people are unconscious and their breath slows or comes to a stop, they use smelling salts to revive them? Well a smelly sock (そく) can work just as well. Socks get really stinky and their stench is powerful enough to revive someone who isn’t drawing breath.