Sudden cardiac death due to a heart rhythm disturbance after a heart attack (myocardial infarction) is a common cause of death. It is well documented that sudden cardiac death after a myocardial infarct (MI) is associated with low or poor heart rate variability (HRV). HRV is a measure of beat-to-beat changes in heart rate, with a greater variation associated with a "healthier" heart. The effect of caffeine on HRV in patients at high risk for sudden cardiac death is unknown. We, the investigators at the Royal Bournemouth Hospital, aim to study the effect of coffee or tea on HRV after MI.