Mammals have four chambered hearts, and if I recall correctly, blood
goes into the right atrium, the right ventricle, then to the lungs,
then to the left atrium, left ventricle, and finally the rest of the
body.

But what about the hearts other vertebrates?  I seem to remember birds
have a three chambered heart--how does this work?  (I'm also curious
about the hearts of reptiles, amphibians, and fish.)

(This was a homework question, oh, 15 years ago, but I couldn't find
the answer and so wasn't able to turn in the report, and wrote on
heart attacks instead.)

Dear purpleanemone-ga,
I can do no better than quote the answer direct from this excellent
web page (Estrella Mountain Community College). The article discusses
all types of circulatory systems. It provides excellent diagrams
including the course of oxygenated blood, deoxygenated blood and mixed
blood through various heart systems and discusses the differences.
The page takes time to load because of the diagrams, but once it has
go to the "Vertebrate Vascular Systems" section halfway down.
"Humans, birds, and mammals have a 4-chambered heart that completely
separates oxygen-rich and oxygen-depleted blood. Fish have a
2-chambered heart in which a single-loop circulatory pattern takes
blood from the heart to the gills and then to the body. Amphibians
have a 3-chambered heart with two atria and one ventricle. A loop from
the heart goes to the pulmonary capillary beds, where gas exchange
occurs. Blood then is returned to the heart. Blood exiting the
ventricle is diverted, some to the pulmonary circuit, some to systemic
circuit. The disadvantage of the three-chambered heart is the mixing
of oxygenated and deoxygenated blood. Some reptiles have partial
separation of the ventricle. Other reptiles, plus, all birds and
mammals, have a 4-chambered heart, with complete separation of both
systemic and pulmonary circuits."
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookcircSYS.html

Please ask for clarification of any part of this research before
rating the answer.

answerfinder-ga

Search strategy
"three chambered heart" diagram
://www.google.com/search?q=%22three+chambered+heart%22+diagram&hl=en&lr=&ie=UTF-8&oe=UTF-8&start=10&sa=N