Researchers Find Why Viagra May Likely Help Patients with Heart Failure

In a new study that will be published in the July 17th issue of the journal Circulation, Canadian researchers reveal that the erectile dysfunction drug Viagra (Sildenafil), may likely be effective in the treatment of patients with right-sided heart failure, principally because their study shows that only the hearts of these patients exhibit the target molecules that can be blocked by these types of drugs.

The study was led by Drs. Jayan Nagendran, a cardiac surgery resident and Evangelos Michelakis, professor in the Department of Surgery and the Department of Pharmacology at the University of Alberta in Canada.

The researchers wanted to gain insight into the mechanism of how Viagra may benefit patients with pulmonary hypertension (high blood pressure in the lung vessels). This devastating condition usually leads to right-sided (right ventricle) heart failure.

In their study, the researchers evaluated heart specimens from 9 patients to assess their phosphodiesterase type-5 (PDE-5) activity and their response to specific type-5 PDE inhibitors such as Viagra.

PDE-5 is an enzyme that degrades the activity of cGMP, a chemical that relaxes smooth muscle cells. In the vasculature, relaxation of smooth muscle cells causes vessels to dilate thereby increasing blood flow.

PDE-5 is preponderant in the corpus cavernosum of the penis. When it's inhibited, it leads to higher cGMP levels and less dilation (more constriction) of the blood vessels that let blood escape from the corpus cavernosum and thereby leading to a sustained erection.

The researchers essentially found that PDE-5 was not expressed in heart samples from patients that were healthy. Conversely, they did discover that patients with enlarged right heart ventricles had marked increased PDE-5 activity.

When the research team used Viagra (the PDE-5 inhibitor) in their experiments, they found that it increased the activity of isolated cardiac cells and the strength of heart contractions only in unhealthy samples and patients and not in any of the healthy controls.