Cenforce 100mg Patients who have suffered a heart attack or other heart problems, high or low blood pressure or low blood clotting. Anyone who has an allergic reaction to sildenafil. Anyone taking medications that contain nitric oxide or nitrates that are used, including in some cases of angina (chest p*in). The most commonly used nitrates include nitroglycerin and isosorbide dinitrate. If you suffer from angina and are not sure whether your medication corresponds to any of the above, consult your doctor before taking the drug.