Final answer:
Cardiac output is directly proportional to both heart rate and stroke volume, as an increase in one or both will result in increased cardiac output.
Step-by-step explanation:
Cardiac output is directly proportional to both heart rate and stroke volume. This means that an increase in either of these factors will lead to an increase in cardiac output, which is the volume of blood pumped by the heart in one minute.
It is computed as the product of heart rate, the number of heart contractions per minute, and stroke volume, the volume of blood pumped into the aorta per contraction of the left ventricle.
Therefore, cardiac output can be augmented by increasing heart rate, which commonly occurs during physical exercise, or by increasing stroke volume, which can occur if the heart contracts with more force or more blood returns to the heart between contractions.