Is fever an indicator of an increase in cardiac output?

Increased pulse. When one has a fever, the body usually responds with vasodilatation (widening of blood vessels) to be nearer the outside of your body and let the heat dissipate. With widening of the vessels the heart must increase the pulse rate to maintain proper blood pressure. There is much more to this and an md can fill you in.
No but it is a cause. Fevers cause your heart rate to increase. Cardiac output is determined by heart rate x stroke volume. So if you increase hr you increase cardiac out put.