Sildenafil should never be used by individuals taking any kind of nitrate drug (e.g. nitroglycerine
) as it can cause potentially life-threatening low blood pressure. Individuals with heart problems are at increased risk of cardiovascular side-effects such as heart attack, stroke, chest pain, high blood pressure and abnormal heart beat. Other side-effects include headache, facial flushing, indigestion, dizziness, abnormal vision, and hearing loss.