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==Caffeine and Myocardial Blood Flow ==
200mg of caffeine does not change the myocardial blood flow at rest, but during exercise it significantly reduces it<ref name="Namdar-2009"/><ref name="Namdar-2006"/>. This decrease in myocardial blood flow is worse at altitude<ref name="Namdar-2006"/> and in people with Coronary artery disease<ref name="Namdar-2009"/>. This change in myocardial blood flow is not a risk factor for healthy individuals<ref name="Namdar-2009"/><ref name="Namdar-2006"/>, but for those with Coronary artery disease the combination of caffeine and exercise may exacerbate their condition.
==Caffeine and Irregular Heart Beats==
[http://en.wikipedia.org/wiki/Cardiac_arrhythmia Cardiac arrhythmias] (irregular heartbeats) are a group of conditions where the heart does not beat normally and can be a life threatening emergency. There is a common belief that caffeine is linked to some types of arrhythmias, but this does not seem scientifically supported for <ref name="RashidHines2006"/><ref name="Katan-2005"/><ref name="Pelchovitz-2011"/>. In fact, an animal study showed that moderate caffeine reduces the risk of atrial fibrillation<ref name="RashidHines2006"/>. A study giving recent heart attacks 450mg of caffeine showed no change in the risk of arrythmia<ref name="Myers-1990"/>. Giving 200mg of caffeine before a bicycle stress test to patients who have malignant ventricular arrhythmias made no difference<ref name="Graboys-1989"/>. Note that a caffeine overdoes can result in heart problems<ref name="Pelchovitz-2011"/>.
==Evaluating the risks==
Because coronary artery disease may not have any initial symptoms<ref name="MayoCAD"/>, risk evaluation is tricky. Some runners who died suddenly had high cholesterol, high blood pressure or chest pains<ref name="WallerRoberts1980"/>. Other risk factors include diabetes, smoking, family history of heart attacks, obesity, long term alcohol use. If you have any risk factors for coronary artery disease, it would be prudent to talk to a healthcare professional.
<ref name="Namdar-2006"> {{Cite journal | last1 = Namdar | first1 = M. | last2 = Koepfli | first2 = P. | last3 = Grathwohl | first3 = R. | last4 = Siegrist | first4 = PT. | last5 = Klainguti | first5 = M. | last6 = Schepis | first6 = T. | last7 = Delaloye | first7 = R. | last8 = Wyss | first8 = CA. | last9 = Fleischmann | first9 = SP. | title = Caffeine decreases exercise-induced myocardial flow reserve. | journal = J Am Coll Cardiol | volume = 47 | issue = 2 | pages = 405-10 | month = Jan | year = 2006 | doi = 10.1016/j.jacc.2005.08.064 | PMID = 16412869 }}</ref>
<ref name="MaronEpstein1986">{{cite journal|last1=Maron|first1=Barry J.|last2=Epstein|first2=Stephen E.|last3=Roberts|first3=William C.|title=Causes of sudden death in competitive athletes|journal=Journal of the American College of Cardiology|volume=7|issue=1|year=1986|pages=204–214|issn=07351097|doi=10.1016/S0735-1097(86)80283-2}}</ref>
<ref name="RashidHines2006">{{cite journal|last1=Rashid|first1=Abdul|last2=Hines|first2=Mujahid|last3=Scherlag|first3=Benjamin J.|last4=Yamanashi|first4=William S.|last5=Lovallo|first5=William|title=The effects of caffeine on the inducibility of atrial fibrillation|journal=Journal of Electrocardiology|volume=39|issue=4|year=2006|pages=421–425|issn=00220736|doi=10.1016/j.jelectrocard.2005.12.007}}</ref>
<ref name="Katan-2005"> {{Cite journal | last1 = Katan | first1 = MB. | last2 = Schouten | first2 = E. | title = Caffeine and arrhythmia. | journal = Am J Clin Nutr | volume = 81 | issue = 3 | pages = 539-40 | month = Mar | year = 2005 | doi = | PMID = 15755819 }}</ref>
<ref name="Pelchovitz-2011"> {{Cite journal | last1 = Pelchovitz | first1 = DJ. | last2 = Goldberger | first2 = JJ. | title = Caffeine and cardiac arrhythmias: a review of the evidence. | journal = Am J Med | volume = 124 | issue = 4 | pages = 284-9 | month = Apr | year = 2011 | doi = 10.1016/j.amjmed.2010.10.017 | PMID = 21435415 }}</ref>
<ref name="Myers-1990"> {{Cite journal | last1 = Myers | first1 = MG. | last2 = Harris | first2 = L. | title = High dose caffeine and ventricular arrhythmias. | journal = Can J Cardiol | volume = 6 | issue = 3 | pages = 95-8 | month = Apr | year = 1990 | doi = | PMID = 1692755 }}</ref>
<ref name="Graboys-1989"> {{Cite journal | last1 = Graboys | first1 = TB. | last2 = Blatt | first2 = CM. | last3 = Lown | first3 = B. | title = The effect of caffeine on ventricular ectopic activity in patients with malignant ventricular arrhythmia. | journal = Arch Intern Med | volume = 149 | issue = 3 | pages = 637-9 | month = Mar | year = 1989 | doi = | PMID = 2465748 }}</ref>
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