Which of the following is an effect of dehydration?

Dehydration reduces plasma volume, making the heart work harder to circulate blood. NASM notes that fluid loss causes cardiovascular strain, often leading to an increased heart rate to maintain cardiac output during exercise. This is due to decreased stroke volume—less fluid in the bloodstream means less blood pumped per beat, so the heart compensates by beating faster. Other effects include impaired thermoregulation, reduced sweat efficiency, and decreased exercise performance. Increased blood volume is not correct (dehydration decreases it), sweat rate often decreases rather than increases when dehydrated (leading to overheating risk), and blood pressure can drop rather than rise in severe dehydration. Therefore, increased heart rate is the hallmark acute cardiovascular response to dehydration during activity.