Which of the following factors would be LEAST likely to affect stroke volume?

Stroke volume, which is the volume of blood pumped by the heart with each beat, is influenced by a variety of physiological factors. Among the choices provided, temperature is typically the least likely to have a direct impact on stroke volume compared to heart size, gender, and duration of contraction.

While temperature can influence overall cardiovascular function, such as affecting heart rate and peripheral resistance, it does not directly modify stroke volume in a significant way. Factors like heart size are crucial because a larger heart can typically pump more blood per stroke, thus influencing stroke volume directly. Gender also plays an important role, as physiological differences, such as average heart size and blood volume, can lead to varying levels of stroke volume between males and females. Duration of contraction is vital as well, since it directly affects how long the heart muscles contract and how much blood is ejected with each heartbeat.

Overall, while temperature can have secondary effects on the cardiovascular system, it does not fundamentally alter the mechanics or capacity of the heart to pump blood, making it the least likely factor to affect stroke volume directly.