Sildenafil has two actions that may be of consequence in patients with heart disease. First, it can lower the blood pressure. Second, it interacts with nitrates.Sildenafil is a vasodilator (that is, a drug that dilates blood vessels), and consequently it lowers the systolic blood pressure (the "top" number in blood pressure measurements) by an average of 8 mmHg. In the majority of patients with heart disease, including most of those being treated with antihypertensive drugs, this is not a problem. Studies have shown that the incidence of side effects (including side effects related to low blood pressure, such as dizziness and fainting) are no higher in users of sildenafil who are also taking antihypertensive drugs.
However, the vasodilating effects of Sildenafil do become potentially hazardous when combined with the vasodilating effects of nitrates, drugs that are still commonly used in patients with coronary artery disease. Patients taking both nitrates and Sildenafil are prone to develop severe hypotension (low blood pressure) and syncope (fainting.) Patients taking nitrates for their coronary artery disease, therefore, should never take Sildenafil. Further, anyone who has taken Sildenafil during the past 24 hours should not take nitrates.
There are some conditions in which the modest drop in systolic blood pressure caused by sildenafil may be dangerous. Patients with severe heart failure accompanied by low blood pressure measurements may become worse if further hypotension is produced. In addition, some patients with hypertrophic cardiomyopathy may become symptomatic if their systolic blood pressure is reduced. Nitrates such as nitroglycerin must be avoided within 24 hours of using Viagra or Levitra and within 48 hours of taking Cialis, according to the recommendations contained in Sexual Activity and Cardiovascular Disease: A Scientific Statement from the American Heart Association.
Men with ED typically have some artery blockage and these drugs work by dilating the blood vessels to improve blood flow. Patients whose artery blockage is severe enough to cause chest pain may be prescribed nitrates — whether in a patch, a long-lasting oral form or a fast-acting nitroglycerin pill placed under the tongue — to alleviate their symptoms.
When the drugs are combined, there may be a powerful reaction, with blood pressure dropping 50, 60 or 80 points in 30 minutes. The mildest side effect might be a feeling of light-headedness, or a patient may faint. A more severe blood pressure drop could trigger kidney failure or a stroke. A patient who visits an emergency department complaining of chest pains should volunteer whether he has taken an ED drug.
Although sexual activity slightly raises the risk of triggering a heart attack, the good news is that for most patients with cardiovascular disease the risk is minuscule, according to Levine.