Question

an increase in venous return will _________ stroke volume and _________ the strength of contraction.
a increase: increase
b increase: decrease
c decrease: decrease
d decrease: increase

Explanation:

Frank - Starling law of the heart states that within physiological limits, an increase in venous return (pre - load) leads to an increase in end - diastolic volume. This causes the cardiac muscle fibers to be stretched (increased pre - load). As a result, the force of contraction (contractility) increases (due to better actin - myosin interaction as the fibers are optimally stretched within the physiological range), which in turn increases the stroke volume (the volume of blood pumped out of the ventricle with each contraction).

Answer:

A. increase; increase