Does it fall? Rise to high levels? Stay normal? All of the above?
Need answer fastish.
I’m not sure about ‘during’ a heart attack or stroke, but an unusually high blood pressure reading can be a symptom of an upcoming MI (myocardial infarction).
- Heart attack - it depends
If there the victim is in a lot of distress (say from the pain of the heart attack itself, or worsening heart function causing fluid build-up in lungs in turn causing both low blood oxygen levels and a panic-provoking sensation of being unable to breath, or sheer panic from simply knowing you may be about to die), there will often be an outpouring of catecholamines (such as adrenalin) into the bloodstream which raise the blood pressure.
On the other hand, if the heart is severely damaged by the heart attack, and/or its function impaired, the blood pressure may drop (since the heart will then not be pumping out forcefully enough to keep the blood pressure up).
And, of course, sometimes the BP doesn’t change much at all during a heart attack.
- Stroke - in the large majority of cases the BP goes up in a stroke (not necessarily ‘sky high’, but higher than normal for that person).
Most strokes are due to clots blocking the arteries (or blocking smaller artery-like structures) in, or going to, the brain. So, teleologically speaking, by raising the BP, the body is trying to “push” blood past the blockage. Somewhat more accurately, the brain swells in and around the area of the stroke and that leads to locally high pressure. Such pressure tends to further impede the flow of blood into the area which is a bad thing. So, to overcome this local high pressure and thereby get blood delivered to the area of the stroke, the blood pressure rises (to force blood and overcome the high pressure in the area which is opposing the flow of blood into it).
It may also be the case that “stress” of the stroke itself raises the BP (see below for mechanism)
Some strokes are due to bleeding into the brain. Usually, high blood pressure has caused (or facilitated) such bleeding. So, the BP will (still) be high when the stroke (i.e. the bleeding) takes place. Further, the “stress” of the bleeding into the brain, causes an extreme “flight or fight” response, which includes the release of catecholamines into the bloodstream in order to raise the BP (note that it makes sense for the “flight or fight” response to increase BP since in a fight you may, for example, lose blood and thus need help maintaing your BP).
To complicate things, sometimes a stroke can be caused by low blood pressure. If your BP drops too low, there won’t be enough of a head of pressure to send blood into brain, and that can cause a stroke. In such a case, the brain is starved for blood (i.e. oxygen) not because of a clot blocking one artery, but because the brain arteries in general aren’t getting enough blood pumped through them.
Thanks, what about pulse? It will be faster or slower?
if blood pressure us such a poor indicator why is it taken doctors/ para medicsduring heart attack investigations. Also the trying to push past a blockade, won’t that also be true of a blocked coronary artery?
By and large, the pulse goes up in both heart attacks and strokes. There are exceptions. For example, some heart attacks are complicated by disturbances of the heart rate and rhythm. And, in severe strokes associated with massive brain swelling (and thus very high pressures inside the skull), there may be a reflex slowing of the heart.
The reason my admittedly inadequate teleological explanation (“blood being pushed through blockages in arteries by having higher blood pressure”) fails for heart attacks is two-fold: 1. the regulation of the blood supply to the brain can be much more dependent on the blood pressure than is the blood supply to other parts of the body (see cerebral autoregulation), especially with a history of previous high blood pressure 2. very often, the adrenalin (catecholamine) response is more profound in the setting of a stroke compared to the setting of a heart attack.
ETA: BP is important to monitor not because it’s a good indicator of stroke or heart attack, but because if it’s too high or too low then it may require treatment independent of anything else.
I personally found the answer below quite useful:
Happy reading 
Do zombies get heart attacks?