You’re probably best off to avoid Viagra altogether. Consult your doctor. The active ingredient in the drug and the nitrates in nitroglycerin pills both work in much the same way, lowering blood pressure to allow improved blood flow. Taking both of these drugs can cause a precipitous drop in blood pressure, which could be life-threatening.
This sharp drop in blood pressure is particularly dangerous for patients who have angina. As blood pressure drops, blood flow to the heart decreases, which can increase the chances of having a heart attack. It should be noted that some angina patients should avoid the physical stress of sexual activity altogether.
While sexual activity is permissible for those with chronic stable angina, those with unstable angina should avoid sex until the causes of their unstable angina have been addressed through cardiac catheterization.