All three drugs work by a similar mechanism, which is to inhibit the destruction nitric oxide. Nitric oxide is important for vascular health. Viagra was originally intended as a cardiovascular medication, but in trials, the erection side effect was discovered. In low daily dose Cialis studies, cardio health markers are improved. So, there may be a benefit which goes beyond enhanced erections with Cialis. The drug companies don't release studies which don't confirm data which they want the public to know about. Some medical professionals think this is the most important consumer fraud today. For example, with some anti-depressants more than 2/3 of studies are withheld. So, while it is certain that studies have been done as the cardio benefits of the ED drugs which shorter blood serum level half lives, those results are not publicly known.