A fib is the atrium contracting so quickly that CO is not as high as it should be. V fib is the ventricle contracting so quickly that CO is not as hight as it should be. In A fib some blood can still get down to the ventricles and they can still pump, even though it is not as efficient because there may not be a full load of blood. With V fib, there is no blood to pump so you die without proper medical intervention.
have you looked in the websites listed on post #39 of this sticky: Any Good IV Therapy or Nursing Procedure Web Sites- any good iv therapy or nursing procedure web sites? some of them do a better job of explaining the arrhythmias. i particularly like the website for the textbook introduction to 12-lead ecg, the art of interpretation (http://www.12leadecg.com/intro/). it has a glossary that defines all kinds of terms:
term: atrial fibrillation (afib)
definition: the chaotic firing of many atrial pacemakers in a totally haphazard fashion. there are no discernible p waves and the qrs complexes appear in an irregularly irregular pattern. the chaotic firing leads to a loss of the atrial mechanical contraction.
term: ventricular fibrillation (vfib)
definition: the chaotic firing of many ventricular pacemakers in a totally haphazard fashion. there are no discernible qrs complexes. the chaotic firing leads to a loss of the ventricular mechanical contraction.