A healthy person who is extremely physically active has a low heart rate because the heart muscle is very strong and does not have to work hard to circulate blood, according to the American Heart Association. Moderate exercise does not have much effect on heart rate.
Low resting heart rates often occur in athletes, states the AHA. Their hearts may beat just 40 times a minute at rest, while the rates for less fit people fall between 60 and 100. The hearts of less fit people must beat faster to accomplish the same tasks. A heart rate that suddenly slows or is accompanied by fainting, dizziness, unconsciousness, weakness or fatigue is a symptom of a medical condition, Healthline notes.
Healthy people's heart rates also go up slightly under certain circumstances. High heat and humidity cause the heart to work harder because it circulates additional blood to help the body cool down, Mayo Clinic explains. Extra blood goes to dilated vessels near the skin surface, and extraneous heat leaves through the skin, reports Columbia University. Under these conditions, pulse rates typically rise five to 10 beats per minute, says AHA.
Standing sometimes marginally increases a healthy person's pulse for a few minutes, but it soon returns to normal, AHA observes. Feelings of stress, anxiety, elation and misery are also able to make the heart work harder.