But you're lucky, relatively speaking. If you were shot in the heart, your blood pressure would quickly drop, but it would take 10 to 15 seconds to lose brain function. In that time you could draw your gun, utter last words, or spend some time thinking about your unfortunate situation.
Caffeine can cause indigestion, which in turn may lead to heart palpitations. However, arrhythmia (abnormal heart rhythm) can also cause palpitations, and this condition is more of a concern. Seek medical attention if your palpitations last longer than two or three minutes.
By speeding up the nervous system, stimulant medications can make you feel jittery and increase your heart rate. The caffeine in green tea might also speed up the nervous system. Taking green tea along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure.