Final answer:
A positive chronotropic drug effect causes a significant increase in heart rate. When heart rate exceeds 160 bpm, cardiac output decreases, and substances like adrenaline increase heart rate.
Step-by-step explanation:
A positive chronotropic drug effect will significantly increase heart rate. The term 'chronotropic' refers to the heart rate, so a positive chronotropic effect implies an increase in the pace at which the heart beats. While several drugs can have varying impacts on heart rate, those classed as positive chronotropes specifically act to raise it.
Looking at related cardiovascular concepts, when the heart rate increases above 160 beats per minute (bpm) in a healthy young adult, cardiac output typically decreases. This is because the time for ventricular filling becomes too short, leading to insufficient stroke volume, even though the heart is beating more frequently. An example of a substance that positively affects heart rate is adrenaline (also known as norepinephrine), which is known to stimulate heart rate and can be considered a positive chronotrope and inotrope.