Heart failure patients represent a group of individuals at higher risk for cardiac arrhythmias. There is a perception that caffeine consumption may represent an increase in this risk. Although the medical staff and health professionals suggest a reduction in the intake of this substance to patients considered at risk, there is no scientific proof for this recommendation.

Some animal studies suggest a possible association between arrhythmias and caffeine use with higher doses, but this finding did not appear in human studies. In particular, little is known about the association between caffeine consumption and arrhythmias in patients with heart failure, especially at higher doses of consumption.

More specific and safe guidelines on caffeine consumption are needed.

Inclusion Criteria:

• Heart failure in NYHA functional class I-III
• LV Ejection fraction <45%
• Age > 18 y.o.
• Cardio-defibrillator implanted with normal functioning with at least 30 days.

Exclusion Criteria:

• Impossibility of take caffeine
• Inability to perform an exercise test
• Initial use of amiodarone in the last 2 months
• Unstable ventricular arrhythmias, shock or ATP in the last 60 days
• Hospitalization in the last two months due to decompensated heart failure