Is the OP making a dictinction between a “heart attack” and stopping or poisoning the heart? Because, if so, few of the proposed methods will produce a “heart attack.”
Potassium chloride stops the heart (it’s used for this purpose in the capital punishment IV cocktail). Excess potassium is easily detected
Calcium promotes arrythymias (which can kill you), but I’ve never read of it stopping the heart or promoting heart attacks. Excess Ca is easily detected
Bicarbonate increases blood pH. This can cause lots of problems, but no direct effect on the heart. Excess Bicarb is easily detected
Adrenaline make the heart pump harder against blood vessels that are increasingly clamped down. The net effect is to make the heart work really hard, while elevating blood pressure to a great degree. Such alterations may promote a heart attack in an otherwise succeptible individual. Excess adrenaline is easily detected, but since it is elevated in the context of a heart attack anyway (the body’s way to try to make the most of a shitty heart), maybe you’d get away with it. But probably not since you’d likely need a quantity inconsistent with any physiological state.
I don’t know what ricin and grayanotoxin do specifically to the heart, but it’s more likely a direct toxicity than promotion of heart attack.
Air embolus can make it impossible for the heart to pump blood, but this works by filling up the heart’s chambers with air, physically impeding the entry of blood. To be effective, the embolus must be massive. The commonly held notion that one lil’ bubble will do you in has been refuted by no lesser a source than the master himself, but I can’t find the vstchinken column. In any case, it’s pretty obvious what happened when you open the heart and find it full of frothy blood.
To answer the OP, I know of no means to produce a perfect, heart attack (short of stuffing an old, fat guy-with a family history significant for heart disease-with french fries and making him run like the wind) While there are things that work (adrenaline, as mentioned and neo-synepherine as well), they are detectable and the evil villian would get pinched. And if I knew of some perfect method, do you think it’d be a good idea to post it here?