Phosphodiesterase 5 inhibitors, such as sildenafil, vardenafil and tadalafil, are now approved for the treatment of erectile dysfunction. They inhibit the cGMP-specific isoform 5 of phosphodiesterase, resulting in cGMP accumulation, which, for example in smooth muscle cells, reduces muscular tone. In the cardiovascular system, they slightly reduce arterial systemic blood pressure. This moderate effect was also shown in combination with many antihypertensive drugs. But the important contraindication is the concomitant use of PDE 5 inhibitors with any drug serving as a nitric oxide donor, as this combination can lead to significant arterial hypotension. Caution is needed in patients on alpha-blocking agents. In general, this class of drugs was not shown to exhibit direct deleterious effects on the myocardium or promote arrhythmias. Furthermore, statistical evaluations did not demonstrate an increased risk for patients taking PDE 5 inhibitors in comparison with an adequate control population. Many patients suffering from erectile dysfunction may be characterized by multiple cardiovascular risk factors or even ischemic heart disease, suggesting an increased baseline risk. While in many forms of erectile dysfunction, these agents seem to be very effective, it becomes clear that endothelial dysfunction is an attractive target of PDE 5 inhibitors and may also be the underlying cause in many types of erectile dysfunction. In addition, these agents seem to be very effective in lowering pulmonary arterial pressure, which might provide the opportunity to treat primary and some forms of secondary pulmonary hypertension, perhaps in combination with inhaled nitric oxide or other pulmonary arterial vasodilators. Sildenafil was approved for treatment of primary arterial hypertension in the U.S. in June 2005. Recently, direct cardioprotective effects were described in animal research, resembling preconditioning-like effects, which may, under certain conditions, also be applicable in clinical research.