You know this because? Making up a claim out of thin air is not a factual statement. You are claiming out of all the chemical compounds that can possibly exist in the world, there doesn't exist one which is likely to cause a delayed heart attack which is currently undetectable. What do you think researchers at bioweapons lab do all day?
Ever taken basic courses in biology?
There are only two possibilities for such toxins: chemical or biological.
Chemical toxins work by interacting/interfering with body chemistry. A chemical toxin that has a delayed effect on the order of days, as opposed to minutes, has no theoretical basis in science. What is the chemical doing during the delay? What would prevent it from acting immediately? Drugs can be made with delayed effects by coating it with a slow dissolving substance, but we're talking about something you can slip into food or drink here.
A biological toxin could theoretically have a delayed effect, but it is extremely uncontrollable. The channel of infection also determines the nature of the toxin. Ingested biological agents would have to be able to move out of the digestive tract and into the blood stream in order to cause a myocardial infarction effect as described, and that is simply unknown to current science. Airborne agents would be too volatile and indiscriminate, infecting everyone in the area, this defeating the very purpose of the attack, which is to make it look like an accident. Worse, any biological toxin can be easily detected with blood work or at worst, an autopsy, making it impossible to look like a natural death.
There is a third possibility, radiation poisoning. It has the delayed effect that you seek, but radiation works by destroying cells. You cannot cause heart attacks with it and it's going to be extremely obvious.
Just to add, it's a lot harder to poison someone than you think. One simple security precaution would be to ensure nobody from the food preparation unit knows who they are preparing the food for. Have trusted agents bring the food to the VIP.
