When you are wide awake and or feeling bored at home. Never exercise right after a meal (might feel like throwing up).
Infections do not cause heart attacks mostly.... heart attacks maybe due to clogged artery,vein or high blood pressure etc.
Many muscles in pairs are made of an extensor muscle and also a flexor muscle. Together, this grouping will allow you to stretch and relax a muscle.
Pepsin I believe is the answer