Caffeine can affect the heart by raising levels of epinephrine, which increases blood pressure, heart contractility, and heart rate. In high doses, caffeine can cause abnormal heart rhythms or palpitations in susceptible individuals. However, for most people caffeine's effects on the heart lessen with regular use as tolerance develops. Moderate caffeine intake through sources like coffee in amounts around 3-6 mg per kg of body weight has been shown to improve exercise performance and endurance without harmful effects. Those with heart conditions should consult a doctor before using caffeine for exercise.

1. Caffeine, Your Heart and Exercise
By T. Jared Bunch, MD
One of the most common comments that I receive in
seeing a new patient with a heart rhythm disorder is
“when my heart started racing (or skipping beats) I
stopped drinking anything with caffeine.” There seems to
be a general perception that caffeine can irritate the
heart. The use of caffeine may be at an all-time high in
today’s society as it is in many drinks, energy
supplements, exercise regiments, coffee, and some teas.
Caffeine is a natural product that is extracted from the
raw fruit of coffee plants (over sixty species), kola nuts,
cocoa, yerba maté, guarana berries, coffee beans and
teas. Caffeine is rapidly absorbed in about 30-60 minutes
in our bodies after ingestion.
Caffeine and Your Heart
The question behind the comment I often encounter in
clinic is “does caffeine effect my heart?” The simple
answer is that it does. Caffeine in high doses raises your
blood level of epinephrine. Epinephrine is also known as
adrenalin. In pure forms, epinephrine can increase blood
pressure, increase the contractility or force of the heart,
and mildly increase the heart rate. In patients that are
susceptable to abnormal heart rhythms, high doses can
cause the heart to develop skipped beats from the upper
or lower heart chambers or palpitations from a rapid heart
rhythm (1).
In most patients that I meet, when high doses of caffeine
are consumed, there can be an uncomfortable feeling of
the heart beating. This is usually due to a mildly elevated
heart rate and increased force of each heartbeat. These
are normal responses of the heart when exposed to
epinephrine, but they can lead to uncomfortable
symptoms. With normal heart responses the symptoms
typically improve when the body levels of caffeine
diminish. Unfortunately, if the caffeine causes the heart to

2. beat abnormally, the abnormal heart rhythm can persist
even after the body levels of caffeine are very low or even
absent.
For most people that enjoy caffeinated products our
bodies develop tolerance to caffeine over time and the
effects on the heart are lessened. Unfortunately for most
patients that have consumed caffeine for many years
without significant changes, the development of new
abnormal heart rhythms is usually independent of the
caffeine. However, it is always a good idea to consider a
trial of stopping caffeinated products if you experience an
abnormal heart rhythm or any new heart symptoms.
When considering your caffeine courses, caffeine that has
been extracted or developed as a chemical, dry product,
or pill appears to be more potent in our bodies compared
to natural sources of caffeine. For example, the
metabolism and exercise performance effects with
caffeine are greater with caffeine pills compared to coffee
that has a similar level of caffeine (2).
Caffeine and Exercise
There are many studies that have examined the impact of
caffeine during exercise. When interpreting these studies
you must take into account that they were performed in
people that were often athletes with healthy hearts and
may not apply to people with heart disease. Recently, the
Journal of the International Society of Sports Nutrition
summarized the effects of caffeine on exercise:
“1. Caffeine is effective for enhancing sport performance
in trained athletes when consumed in low-to-moderate
dosages (~3-6 mg·kgBM-1
) and overall does not result in
further enhancement in performance when consumed in
higher dosages (≥ 9 mg·kgBM-1
).
2. Caffeine exerts a greater ergogenic effect [enhancing
exercise performance] when consumed in an anhydrous
state [contains no water or pill form] as compared to
coffee.

3. 3. Caffeine enhances alertness during periods of extended
exhaustive exercise, as well as periods of sustained sleep
deprivation.
4. Caffeine is ergogenic for sustained maximal endurance
exercise, and has been shown to be highly effective for
time-trial performance.
5. Caffeine supplementation is beneficial for high-intensity
exercise, including team sports such as soccer and rugby,
both of which are categorized by intermittent activity
within a period of prolonged duration.
6. The literature is equivocal [unclear or ambiguous]
when considering the effects of caffeine supplementation
on strength-power performance, and additional research
in this area is warranted.
7. The scientific literature does not support caffeine-
induced diuresis [increased urination] during exercise, or
any harmful change in fluid balance that would negatively
affect performance” (3,4).
When you look at the total evidence available, in low to
moderate levels, caffeine will likely result in an
improvement in both your aerobic exercise ability and
tolerance and may also provide benefit in resistance
exercise (4).
In conclusion, if you feel abnormal heart beats or rhythms
if you start using caffeine or start using high doses then
stop using it. You may have to wait days after the caffeine
exposure for your heart to go back to normal. If it doesn’t
or the symptoms are severe, you should contact your
doctor. If you develop these symptoms after years of
using similar levels of caffeine, then your heart symptoms
are likely caused from other sources. If you use caffeine
to improve your exercise ability, use relatively low doses.
The accumulative evidence with low to moderate amounts
of caffeine and exercise suggests it is beneficial and
relatively safe. If you have prior heart disease or
abnormal heart rhythms, talk to your physician before

4. starting an endurance exercise program in which you want
to also use caffeine to enhance your performance.