2. Caffeine. Heart palpitations can occur in people sensitive to
caffeine. If you're one of them, I would still recommend decaf green tea
because of the many health benefits.
3. Nicotine and Alcohol. Both of these are risk factors for
4. Excitotoxins and Free Glutamine. A couple of studies out there have linked glutamate with arrhythias and it is widely reported around the web as well, especially in guys using commercial wheys.  And it makes sense, because they overheat standard wheys which frees up a lot of the glutamate in the whey, turning it into "MSG" effectively. Look at what these authors wrote:
"Central sympathetic stimulation was achieved by intracerebroventricular injection of the excitatory amino acid L-glutamate (10 ï¿½mol), associated with inhibition of nitric oxide synthesis with L-NAME (40 mg/kg, iv). Glutamate triggered ventricular arrhythmia and persistent ST-segment shifts in the ECG, indicating myocardial ischemia." 
Remember that free glutamine (in commercial wheys, autolyzed yeast extract, etc.) has trouble crossing the blood brain barrier, but it is a neurotransmitter and can apparently impact the ventricular nodes of the heart and lead to arrhythmias if levels get high enough. You can probably avoid issues by simply using CFM wheys. Read my links on
Whey and Excitotoxins and Undenatured (CFM) Wheys - A Better Choice.
5. Low Carb Diets. Some men get heart palpitations while on a low carb diet. Researchers have found that the high ketone levels - a low carb diet is sometimes called The Ketogenic Diet - can cause the nodes in the heart to struggle, something I cover in my page on
Low Carb Diets and Arrhythmias.
6. DHEA. Ray Sahelian has reported that medium and higher dosages of this supplement can lead to dangerous heart murmurs.
7. Hypoglycemia. One of our the members on the
Peak Testosterone Forum told the story as to how he had some starch and triggered some
arrhythmia. Of course, the healthiest and longest lived cultures on planet earth eat starch, so this did not make sense to me. It turns out there
was more to the story: he was consuming a lot of maltodextrin:
"But recently (2 months ago) I have been having very strange "heartbeats",exaclty the same as many years ago when I was having maltodextrin that was included in a protein shake I used to drink. I called a cardiologist and when I explained him my sympthoms, he told me that I must be eating something that was causing that,that it was not a problem of my heart. Anyway,he asked me about if I was abusing on any starch and when I told him about maltodextrin, he told me that that was the problem. I quit on that and bingo! the problem dissapeared imediately. Now, when I started having the problem again,I checked the ingredients on my actual protein shakes and also I went to forums and a lot o people blame certain whey proteins. I'm testing on switching to Casein and another brand of whey and I think I'm doing better." 
Why was maltodextrin likely the problem? The reasons is that it has an extremely high glycemic index - well over 100! In other words, it really spikes blood sugar and insulin if you take a lot of it and that was what the poster was doing. This very likely sent him into a hypoglycermic state which is linked with these sorts of issues. And, in fact, some recent studies have found that this is the case with hypoglycemic states experienced by diabetics. 
8. Drugs and Supplements. You should be suspicious of almost all
drugs and supplements. Yes, even supplements can zap you, especially those
with ephedrine. 
9. Noradrenaline and Viagra. Anything that increases noradrenaline can increase the
risk of an arrhythmia. These include yohimbe, popular in many supplements,
and Viagra.  In fairness, Viagra has sometimes shown positive changes
in stroke and arrthymia paramters as well. (Discuss with your physician.)
10. Stress, Sleep and Cortisol. Stress is a well-accepted
arrhythmia-inducer. One study of women with breast cancer found that better
sleep improved their cortisol response and, seemingly, reduced arrhythmias on
average.  Researcher in India found a direct correlation between stress
hormone levels in the blood and severity of arrhythmia for example.