Answer: The concern with nitroglycerine is that it has the potential to drop blood pressure. These heart rate ranges are put in for safety. If the heart rate is <60 or >159 you are even more at risk of causing uncompensated hypotension. With a heart rate <60 or >159 (brady or very tachy) the cardiovascular system is already stressed and further insult to the blood pressure is unlikely to be compensated for appropriately.