Final answer:
Positive inotropic activity results in increased cardiac output option (A) due to a boost in the heart's contractility, which raises stroke volume and consequently, cardiac output.
Step-by-step explanation:
The result of positive inotropic activity is A. Increased cardiac output. Positive inotropes increase the strength of the heart's contraction without necessarily affecting the heart rate. This increased contractile strength leads to an increase in the volume of blood the heart pumps with each beat, known as stroke volume. When stroke volume increases, so does cardiac output, which is the amount of blood the heart pumps in a minute calculated by multiplying stroke volume by heart rate.
Drugs like dopamine, isoproterenol, and digitalis are examples of positive inotropes that can increase intracellular calcium levels in cardiac cells, enhancing contractility. Hormones such as thyroid hormones and glucagon also demonstrate positive inotropic effects.