What influences cardiac output?

Multiple things: Cardiac output is the product of heart rate in stroke volume. Thus, an increase in heart rate results in an increase in cardiac output. Stroke volume can be affected by changes in preload, afterload, and contractility (strength of contraction). Preload is "priming the pump". Afterload is the resistance to ejection during systole (contraction).

Cardiac output: Stroke volume times heart rate equals cardiac output. Stroke volume relates to myocardial contractility, vascular resistance, vascular volume, anemia and metabolic state. There are subcomponents to all of these.