luna,
too much OR too little potassium, (among other minerals) can cause
cardiac irregularities, not necessarily arrest.

Actually, from what I've read the problem is more on the digestion
end.  Potassium that is bound up in compounds found in foods (say, in
bananas) is easily digested, but the potassium in pill form is not.

Also, there is a whole safe =range= before you get into unsafe
dosages.  After all, the huge majority of people in this world do not
go around measuring their potassium intake with the idea that they
will stop immediately upon reaching the minimum daily requirement.
They don't say "Ohmigod, 3500 is the MDR and I just ate 3600, I'm
going to die!"  No, they go around eating as much food as it takes to
make them feel full.  Some eat foods with lots of potassium, others
eat little potassium.  Some people will not even reach the MDA
amounts, others will exceed it by a large amount.  The human body has
ways to handle modest amounts of excess potassium.

This is not to say that it is IMPOSSIBLE to get too much and have
heart problems.  It can be done.  But if the "minimum" requirement is
around 3500 mg, (which is itself an AVERAGE, not a "take this or you
die" figure"), you give no yardstick on what the MAXIMUM safe dose is.
Is it twice the minimum (7000 mg)?  Three times the minimum (10500
mg)?  You are waving a big red DANGER flag without giving any sort of
guidelines for where the =danger= point really begins.

Here's what one of the online drugstores (drugstores.com) mentions
about potassium.  You'll notice mention of problems with too little.
You'll notice digestive problems with too much in pill form.  You'll
notice they talk about problems if you already have kidney problems
before you begin.  But they don't talk about your heart stopping of
you have too much.

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Who is likely to be deficient? So-called primitive diets provided much
greater levels of potassium than modern diets, which may provide too
little. Gross deficiencies, however, are rare except in cases of
prolonged vomiting, diarrhea, or use of ?potassium-depleting?diuretic
drugs. People taking one of these drugs are often advised by their
doctor to take supplemental potassium. Prescription amounts of
potassium provide more than the amounts sold over the counter but not
more than the amount found in several pieces of fruit.

How much is usually taken? The best way to obtain extra potassium is
to eat several pieces of fruit per day, as well as liberal amounts of
vegetables. The amount of potassium found in the diet ranges from
about 2.5 grams to about 5.8 grams per day. The amount allowed in
supplements?99 mg per tablet or capsule?is very low, considering that
one banana can contain 500 mg. One should not attempt to achieve
higher potassium levels by taking large numbers of potassium pills.
This concentrated form of potassium can irritate the stomach?a problem
not encountered with the potassium in food.

Are there any side effects or interactions? High potassium intake
(several hundred milligrams at one time in tablet form) can produce
stomach irritation. People using potassium-sparing drugs should avoid
using potassium chloride-containing products, such as Morton Salt
Substitute?, No Salt?, Lite Salt?, and others and should not take
potassium supplements, except under the supervision of a doctor. Even
eating several pieces of fruit each day can sometimes cause problems
for people taking potassium-sparing drugs, due to the high potassium
content of fruit.

Potassium and sodium work together in the body to maintain muscle
tone, blood pressure, water balance, and other functions. Many
researchers believe that part of the blood pressure problem caused by
too much salt (which contains sodium) is made worse by too little
dietary potassium.

People with kidney failure should not take potassium supplements,
except under careful medical supervision.

Are there any drug interactions? Certain medications may interact with
potassium. Refer to the drug interactions safety check for a list of
those medications.

References:

1. Wahr JA, Parks R, Boisvert D, et al. Preoperative serum potassium
levels and perioperative outcomes in cardiac surgery patients. JAMA
1999;281:2203?10.