Erectile dysfunction (ED) in men is amenable to correction with Viagra in a majority of patients. The accumulated experience of prescribing Viagra across the broad continuum of men suffering from ED is sufficient for a meaningful assessment of the safety of Viagra in clinical practice. The use of Viagra necessitates caution in cardiac failure and when used within six months of acute myocardial infarction and stroke. It is inadvisable in patients with unstable angina pectoris. The co-administration of Viagra with organic nitrates, for example, glyceryl trinitrate or isosorbide dinitrate, is unsafe. The relative contraindications to Viagra in cardiovascular disease are uncontrolled hypertension and impaired cardiac reserve. With respect to interactions with other drugs, the potential influence on the metabolism of Viagra by medications that affect the cytochrome-P-450 system does not translate into clinical effects. The vasodilatory properties of sildenafil citrate are largely responsible for unwanted effects. The most common side effects are headache, flushing (due to vasodilation), and dyspepsia (due to relaxation of the smooth muscle of the gastroesophageal sphincter with reflux). In the recommended single-dose range (25-100 mg), the use of Viagra for erectile dysfunction, in the absence of contraindications, is extremely safe provided the drug is taken under proper conditions.