Excess LDL cholesterol in your blood gets deposited in arteries, the blood vessels that feed the heart and brain. These deposits can join with other substances to form plaque, a thick, hard deposit in the blood vessel that leads to atherosclerosis. Plaque can narrow the passageway inside the artery and pinch off the flow of blood to the heart muscle, and to the penis.

Intracavernosal and intraurethral injections are second-line therapy for patients with ED. Alprostadil is the agent most commonly used for intracavernosal injections. The main adverse effects of intracavernosal injections are painful erection, priapism and development of scarring at the injection site.73 Alprostadil is also available as a topical cream in patients who cannot tolerate injections.75
Overall, sildenafil appears to be relatively safe and effective for treatment of ED in men with stable cardiovascular disease who are not taking NO-donor medications. In a study of 105 men with ED and known or likely coronary artery disease, patients underwent symptom-limited supine bicycle echocardiography 2 times after receiving either sildenafil or placebo.63x63Arruda-Olson, AM, Mahoney, DW, Nehra, A, Leckel, M, and Pellikka, PA. Cardiovascular effects of sildenafil during exercise in men with known or probable coronary artery disease: a randomized crossover trial. JAMA. 2002; 287: 719–725
Crossref | PubMed | Scopus (174) | Google ScholarSee all References All these men had ED and twice underwent symptom-limited supine bicycle exercise echocardiography 1 hour after taking either sildenafil (50 mg or 100 mg) or placebo. This study found no significant changes in resting heart rate, diastolic blood pressure level, or wall motion score index, and the exercise capacity of the 2 groups was similar. Both groups had similar numbers of patients who experienced dyspnea and/or chest pain, had a positive exercise echocardiographic test, and had exercise-induced wall motion abnormalities. Sildenafil caused a mean decrease of 7 mm Hg in the resting systolic blood pressure level compared with the placebo group. In conclusion, this study showed that in patients with stable coronary artery disease, sildenafil caused no change in symptoms, exercise endurance, or presence/extent of exercise-induced ischemia as measured by exercise echocardiography.
The use of shock wave therapy has revolutionized the treatment of many aspects of medicine. High intensity extracorporeal shockwave therapy has been used for the treatment of nephro-urolithiasis while medium intensity shockwave therapy is used by orthopaedic surgeons to treat joint pain as well as tendinitis. Low intensity shockwaves therapy was first noted to improve ischaemia-induced myocardial dysfunction in animal studies when low intensity shockwaves were applied to porcine myocardium (13). Shockwaves induces a localized stress on cell membranes in the same way that shear stress affects endothelial cell membranes (14) and this triggers the release of angiogenic factors, such as increased NO production through increased activity of endothelial NO synthase (eNOS) and neuronal NO synthase (nNOS), platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) (15). These shockwaves also cause membrane hyperpolarization (16), activation of the Ras signaling pathway, non-enzymatic synthesis of NO and induction of stress fibers and intercellular gaps (17).
Cavallini, G., Modenini, F., Vitali, G., & Koverech, A. (2005, November). Acetyl-L-carnitine plus propionyl-L-carnitine improve efficacy of sildenafil in treatment of erectile dysfunction after bilateral nerve-sparing radical retropubic prostatectomy. Urology, 66(5), 1080-5. Retrieved from http://www.sciencedirect.com/science/article/pii/S0090429505006515

For many men, stopping smoking is an erectile dysfunction remedy, particularly when ED is the result of vascular disease, which occurs when blood supply to the penis becomes restricted because of blockage or narrowing of the arteries. Smoking and even smokeless tobacco can also cause the narrowing of important blood vessels and have the same negative impact. 
PubMed | Google ScholarSee all References This prolonged excretion half-life produces enhanced erections up to 36 hours after oral dosing, thereby potentially allowing for more spontaneous engagement of intercourse. The efficacy of tadalafil in the treatment of ED has been proved in randomized double-blind, placebo-controlled trials.78x78Porst, H, Padma-Nathan, H, Giuliano, F, Anglin, G, Varanese, L, and Rosen, R. Efficacy of tadalafil for the treatment of erectile dysfunction at 24 and 36 hours after dosing: a randomized controlled trial. Urology. 2003; 62: 121–125

Nebivolol seems to have an advantage over other beta-blockers when used to treat men with hypertension and ED. It has additional vasodilating effects because it stimulates endothelial release of nitric oxide (NO), resulting in relaxation of smooth muscle in the corpus cavernosum, allowing penile erection.25 Despite limited studies, nebivolol does not seem to worsen erectile function and some studies have demonstrated significant improvement in erectile function with nebivolol compared with second-generation cardioselective beta-blockers.23,26–28

Prescription drugs called “oral phosphodiesterase-5 (PDE5) inhibitors” are considered the “first-line non-invasive treatment” options for patients with ED. These include the drugs that go by brand names: Sildenafil, Vardenafil or Tadalafil. They work by helping the smooth muscle cells lining the blood vessels that supply the penis with blood to work properly. This allows a man to maintain an erection more easily.
These medications don’t work for everyone but they are easy to use and work for around 60% of people who try them. They work by making it easier to get an erection by reducing the effect of (inhibiting) the chemical PDE-5. This chemical is used in the body to make sure there isn’t too much blood in the penis during an erection, but if you have erectile dysfunction then this chemical ends up over-compensating.
First of all, libido (sexual desire) triggers a sympathetic (adrenaline-dependent) nervous system reaction mediated through the thoracic spinal cord. Also important is tactile stimulation, the pleasurable effect of touch, which is mediated through the acetylcholine-dependent parasympathetic nervous system. Both the sympathetic and parasympathetic forces regulate the release of nitric oxide—the universal artery-relaxing agent—from the cells lining the penile arteries and all its smaller branches. Nitric oxide causes the arteries to enlarge, increasing blood flow into the penile tissues. This is followed by compression of blood-draining penile veins, which causes blood to engorge the penis and create an erection.4
A recent systematic review and meta-analysis of relevant studies in this field confirmed that erectile dysfunction is associated with increased risk of CV events and all-cause mortality[89]. The pooled relative risks were 1.44 (95%CI: 1.27-1.63) for total CV events, 1.19 (95%CI: 0.97-1.46) for CV mortality, 1.62 (95%CI: 1.34-1.96) for myocardial infarction, 1.39 (95%CI: 1.23-1.57) for cerebrovascular events, and 1.25 (95%CI: 1.12-1.39) for all-cause mortality, for men with vs without erectile dysfunction. Of note, the relative risk was higher in intermediate-compared with high- or low-CV-risk populations and with younger age, with obvious clinical implications. Interestingly, the relative risks were higher when erectile dysfunction was diagnosed with the use of a questionnaire compared with a single question (RR = 1.61; 95%CI: 1.38-1.86 vs RR = 1.27; 95%CI: 1.18-1.37, respectively; P = 0.006).
A deficiency of L-arginine, however, does not generally disrupt nitric oxide synthesis because L-arginine availability is not the rate-limiting step in this process. In fact, research over the past five years has identified an endogenous (occurs in the body naturally) inhibitor called “asymmetric dimethylarginine” or ADMA, an amino acid which blocks the production of nitric oxide. By acting as an L-arginine mimic, this damaging look-alike effectively elbows out L-arginine and pushes it off to the side in the biochemical pathway leading to the synthesis of nitric oxide. ADMA is relatively elevated in patients with hypertension, high levels of cholesterol, triglycerides, homocysteine and low-density lipoprotein (LDL), and low levels of high-density lipoprotein (HDL), as well as with aging itself. This inhibitor of nitric oxide synthesis may very well be the common factor shared by all of these abnormal conditions. Increased levels of this detrimental inhibitor (ADMA) block nitric oxide production, leading to endothelial dysfunction.
Faced with concern about ED pills and the heart, the FDA has urged caution in patients who have suffered heart attacks, strokes, or serious disturbances of the heart's pumping rhythm in the previous six months, in men with a history of congestive heart failure or unstable angina, and in men with low blood pressure or uncontrolled high blood pressure (above 170/110 mm Hg). Because certain medications can boost the blood levels of these drugs, men taking erythromycin or certain antifungal or anti-HIV medications should use only low-dose PDE-5 inhibitors. Reduced dosage is also important for men with advanced age and for those with significant kidney or liver disease.
Abstract | Full Text | Full Text PDF | PubMed | Scopus (56) | Google ScholarSee all References Cardiologists use METs of oxygen consumption to compare the energy expenditure of different forms of activity.51x51DeBusk, R, Drory, Y, Goldstein, I et al. Management of sexual dysfunction in patients with cardiovascular disease: recommendations of the Princeton Consensus Panel. Am J Cardiol. 2000; 86: 62F–68F
Abstract | Full Text | Full Text PDF | PubMed | Scopus (30) | Google ScholarSee all References Increased cGMP levels cause intracellular calcium levels to decrease, resulting in relaxation of the corporeal smooth muscle, active dilatation of the penile arteries, arterioles, and sinusoids, and finally, increased arterial inflow and passive compression of penile venous outflow.10x10Kloner, RA and Zusman, RM. Cardiovascular effects of sildenafil citrate and recommendations for its use. Am J Cardiol. 1999; 84: 11N–17N
Get your diabetes under control. According to Dr. Nehra, the most important number you need to stay on top of is your A1C, which is a blood test that lets you know how well your blood sugar has been controlled for the past few months. Lifestyle changes can help and so can medications. Diabetes medications do not add to your risk for erectile dysfunction, says Nehra.
Erectile dysfunction means that a man is not able to have sex because he cannot get or keep an erection. Erectile dysfunction affects >30% of men between 40 and 70 years of age. There are several different causes of ED, including depression, low testosterone, nerve problems, and some medications, but the most common cause is a problem with the blood vessels called atherosclerosis.
According to the Mayo Clinic, oral medications are usually the first-line treatment for ED. Those medications include Sildenafil (Viagra), vardenafil (Levitra, Staxyn), tadalafil (Cialis) and avanafil (Stendra). They operate by helping relax muscles in the penis by strengthening the effects of nitric oxide, a naturally occurring chemical in the body. The drugs increase blood flow to allow patients to get an erection.
To understand what happens in ED, it's helpful to know some anatomical basics. When aroused by either sensory or mental stimuli, the brain sends a signal through the nerves to the penis, causing the muscles there to relax. This opens up space for blood to flow in and engorge the penis. A membrane within the penis traps blood inside to help maintain the erection, which subsides when the penile muscles contract, forcing blood back into the rest of the body. Any number of things can go wrong in this process, leading to erectile dysfunction.
Abstract | Full Text | Full Text PDF | PubMed | Scopus (95) | Google ScholarSee all References Sildenafil has a 4000-fold increased selectivity for PDE-5 over PDE-3, has negligible effects on heart rate, and has only a modest effect on blood pressure level in healthy persons, with an average systolic pressure decrease of 10 mm Hg with a single dose of 100 mg.3x3Zusman, RM, Morales, A, Glasser, DB, and Osterloh, IH. Overall cardiovascular profile of sildenafil citrate. Am J Cardiol. 1999; 83: 35C–44C

Although a considerable number of patients report penile pain with IC injection therapy, it appears that diabetic men still have high compliance rates with therapy. In one study, 16 of 18 diabetic men continued IC injection therapy for 7 years, compared to 7 of 22 nondiabetic control subjects with ED.57 One possible explanation for this is that diabetic patients with ED have fewer options than do nondiabetic men with ED, who are more likely to have a successful response to oral PDE-5 agents, as documented in one study.58 Another explanation is the greater familiarity with needles and injections among men with diabetes than among their nondiabetic counterparts.
Yet another common erectile dysfunction treatment that can be used in combination with oral drugs is a vacuum pump. This device consists of a plastic cylinder, a pump, a set of constriction bands, and a water-soluble lubricant. The lubricant is applied to the base of the penis to help form an airtight seal. The cylinder is placed over the flaccid penis and held tight against the pelvis. The pump is used to create a vacuum within the cylinder, drawing blood into the penis. Once the penis is engorged with blood, a constriction band is rolled off the cylinder to near the base of the penis. The constriction band is helpful for men with venous leakage, in which blood flows out of the penis as fast as it flows in. However, it should be left on for no more than 30 minutes at a time.
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