: Should people with tachycardia avoid caffeine? Well, caffeine increases the resting heart rate. If the resting heart rate of a person with tachycardia is 110 bpm, it may increase to 125 bpm after consuming 200 mg caffeine.

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A regular caffeine consumer will likely develop a partial or complete tolerance to many caffeine effects and side effects, including increased heart rate. Tolerance develops within few days of regular caffeine consumption and disappears within few days of caffeine discontinuation.

Tolerance to the Humoral and Hemodynamic Effects of Caffeine in Man (PubMed Central, 1981)

Acute caffeine in subjects who do not normally ingest methylxanthines
leads to increases in blood pressure, heart rate, plasma epinephrine,
plasma norepinephrine, plasma renin activity, and urinary
catecholamines. Using a double-blind design, the effects of chronic
caffeine administration on these same variables were assessed. Near
complete tolerance, in terms of both humoral and hemodynamic
variables, developed over the first 1-4 days of caffeine. No
longterm effects of caffeine on blood pressure, heart rate, plasma
renin activity, plasma catecholamines, or urinary catecholamines could
be demonstrated.

A single caffeine dose may increase blood pressure but not necessary heart rate in individuals with supraventricular tachicardia.

A prospective placebo controlled randomized study of caffeine in patients with supraventricular tachycardia undergoing electrophysiologic testing (Wiley Online Library, 2015)

Caffeine, at moderate intake (5 mg/kg), was associated with
significant increases in systolic and diastolic blood pressures, but
had no evidence of a significant effect on cardiac conduction and
refractoriness. Furthermore, no effect of caffeine on SVT induction or
more rapid rates of induced tachycardias was found.

the resting heart rate was not significantly different between both
groups [caffeine vs placebo].

Caffeine and Cardiac Arrhythmias: A Review of the Evidence (The American Journal of Medicine, 2011)

Overall, the data suggest that in most patients, even those with known
or suspected arrhythmia, caffeine in moderate doses is well
tolerated and there is therefore no reason to restrict ingestion of
caffeine. Care should be taken to avoid caffeine in situations in
which catecholamines are thought to drive the arrhythmia, as well as
in patients who note sensitivity to caffeine.

Now, I personally cannot claim if caffeine consumption is or is not dangerous for individuals with tachycardia, but most doctors, for example, from American Heart Association) still advise them to cut it down.