Can low or high blood pressure cause a heart attack?

High blood pressure (BP) can cause injury to almost all the major organs of the body. Commonly involved organs are the Kidneys, Brain, and the Heart. The damaging effect of high BP can be seen in two different scenarios:

1. High BP that causes damage over time: Even a modest increase in BP, if left untreated, leads to organ damage over the years, akin to a constant stream of water eroding the rock over the years. Such type of injury may not produce any symptoms until very late in the disease course when major damage has already occurred. Such damage is often irreversible. In the case of the heart, uncontrolled BP over a long period leads to heart failure. 
2. Immediate damage due to very high BP: If blood pressure rises very high very quickly, it can cause immediate injury to body organs. Here, the systolic BP is often >180 mm Hg. It can cause major catastrophes like a heart attack or a brain haemorrhage. Such scenarios are life-threatening and call for immediate medical attention.

Low BP can also cause a heart attack by compromising blood flow into the heart. A normal variation in blood pressure where systolic BP occasionally falls below 90 will not cause a heart attack. Low BP leading to a heart attack is often below 85 mm Hg and is typically in relation to some other concurrent medical problem which is the cause of low BP like severe infection or bleeding. More commonly, it is a heart attack that causes low BP due to a reduction in the pumping power of the heart.

In our routine life, if someone is healthy and is not taking any BP-lowering medicines, there is almost a negligible probability of getting a heart attack due to low BP. On the contrary, a person may get a heart attack causing weakening of the heart muscle which in turn can lead to low BP. Either way, if your systolic BP falls below 85 mm Hg or you have dizziness at any blood pressure, you should seek urgent medical attention.

As you may note, I have skipped discussing diastolic blood pressure (the lower number when you check your blood pressure) as it is not particularly relevant for this write-up.