Any heart problems including angina, chest pain, heart failure, irregular heartbeats, heart attack (myocardial infarction), left-ventricular outflow obstruction, cardiomyopathy or valvular heart disease (e.g. aortic stenosis)
Stroke
Sight loss due to poor circulation
Sight loss because of non-arteritic anterior ischemic optic neuropathy (NAION)
Blood problems such as haemophilia, sickle cell anaemia (an abnormality of red blood cells) or leukaemia (cancer of the blood cells)
Stomach ulcers (e.g. peptic/gastric ulcer)
Liver problems
Kidney problems
An erection that lasted more than 4 hours
Any physical condition affecting the shape of the penis (e.g. angulation, Peyronie's disease, or cavernosal fibrosis)
An inherited eye disease such as retinitis pigmentosa
Multiple myeloma (cancer of the bone marrow)
Galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption
Any serious medical condition that may require immediate hospitalisation.