Men inadvisable to sexual activity due to underlying CV diseases, MI & stroke or life-threatening arrhythmia w/in the last mth; resting hypotension (BP <90/50) or HTN (BP >170/110); cardiac failure or CAD causing unstable angina; retinitis pigmentosa. Hepatic & severe renal impairment; patients w/ anatomical penis deformation or hematologic disorders predisposing to priapism. Patients who experience dizziness or visual disturbances should not drive or operate machinery.