Final answer:
Factors that influence heart rate have a chronotropic effect, with positive chronotropic effects increasing heart rate and negative ones decreasing it. This statement is true. Excessive heart rates can lead to decreased cardiac output due to inadequate ventricular filling time.
Step-by-step explanation:
Mechanisms that affect cardiac rate are indeed said to have a chronotropic effect. This is true. Factors that increase the heart rate, like sympathetic nervous system stimulation, thyroid hormones, and substances like epinephrine, have a positive chronotropic effect. Conversely, factors like ß-blockers, which inhibit the actions of the sympathetic nervous system by binding to its receptors, have a negative chronotropic effect, causing a decrease in heart rate. In the case of excessive heart rates, such as increases above 160 bpm in a healthy young adult, cardiac output may actually decrease due to a shortened diastolic filling time and reduced stroke volume.