Changes in heart rate or rhythm are called
arrhythmias. They may reduce the amount of blood flow
from the heart (cardiac output) to the brain and the rest of the body.
Decreased blood flow to the brain can cause you to pass out suddenly (syncope). In some cases, you may feel short of breath
or have
palpitations or chest discomfort before you faint.
Heart rate or rhythm changes also can occur when you are anxious or
afraid or in a stressful situation. Feeling worried, anxious, and nervous may
increase your heart rate, and you may feel lightheaded or as though you are
going to faint.
Changes in heart rate or rhythm that cause fainting can be
life-threatening. If you have these symptoms, call your health professional for
an evaluation.
If you have heart disease, heart failure, or have had a heart attack,
it is especially important to understand the seriousness of a change in your
heart rate or rhythm. Call your health professional immediately if you have a
sudden change in your usual heart rate or rhythm and you feel faint or
lightheaded.