Final answer:
The most likely immediate cause of death in this case is arrhythmia.
Step-by-step explanation:
The most likely immediate cause of death for the 56-year-old man in this case would be arrhythmia. An acute myocardial infarction (heart attack) can disrupt the normal electrical activity of the heart, leading to abnormal heart rhythms or arrhythmias. These arrhythmias can be life-threatening and can result in sudden cardiac arrest and death.