What is the smallest creature that has a heart etc?

Answer 1

Dicopomorpha echmepterygis is a parasitic wasp in the family Mymaridae. The males of this species are the smallest of all known insects. They are blind and wingless and may be no more than 0.139 mm in length (smaller than a single-celled paramecium). Females are 40% larger. Obviously, the eggs and larvae of this wasp are considerably smaller than the adult.

This species from Illinois is an idiobiont parasitoid of the eggs of a lepidopsocid barklouse, Echmepteryx hageni. The adult males mate with their sisters inside the host egg, and die without ever leaving the egg; similar life histories can be found in the wasp family Trichogrammatidae, also in the superfamily Chalcidoidea.

http://en.wikipedia.org/wiki/Dicopomorpha_echmepterygis

Answer 2

The smallest creature with a heart is the fairyfly, a type of parasitic wasp. Their hearts are very small, but they are still functional in pumping blood throughout their tiny bodies.