I agree, anytime you are using a stimulant it messes with the old ticker and can be dangerous.
Here's a few things to look at:
http://coffeefaq.com/caffaq.html#WhatHappens
Basically, overdosing on caffeine will probably be very very unpleasant but not kill or deliver permanent damage.
However, People do die from it.
<DL><DT>Toxic dose <DD>
The LD_50 of caffeine (that is the lethal dosage reported to kill 50% of the population) is estimated at 10 grams for
oral administration. As it is usually the case, lethal dosage varies from individual to individual according to weight. Ingestion of 150mg/kg of caffeine seems to be the LD_50 for all people. That is, people weighting 50 kilos have an LD_50 of approx. 7.5 grams, people weighting 80 kilos have an LD_50 of about 12 grams.
In cups of coffee the LD_50 varies from 50 to 200 cups of coffee or about 50 vivarins (200mg each).
One exceptional case documents survival after ingesting 24 grams. The minimum lethal dose ever reported was 3.2 grams
intravenously, this does not represent the oral MLD (minimum lethal dose). In small children ingestion of 35 mg/kg can lead to moderate toxicity. The amount of caffeine in an average cup of coffee is 50 - 200 mg. Infants metabolize caffeine very slowly.
</DD></DL>
http://medweb.rcm.upr.edu/publications/sidney_kaye/toxicology-of-caffeine.htm
No deaths have been reported by an overdose of drinking coffee, - but an overdose of coffee of more than 5 cups per day may have a direct dose related effect on the central nervous system, and may affect the heart and its rhythm, blood vessel diameter, coronary circulation and increase blood pressure, urine volumen and gastric secretions. These effects are capable of producing bizarre signs and symptoms which are very baffling, i.e.: High fever or low grade fever unresponsive to persistent antibiotic treatment (3), psychoneurosis (anxiety) unresponsive to Diazeparn (1) and paraxysmal atrial tachycardia (4).
But it's still better than
:smoker2: