The mechanisms by which testosterone plays a role in erectile function are not completely understood. A study evaluating the effect of testosterone on erections in surgically castrated rabbits and control animals, in which the rabbits’ intracavernosal pressures were compared after cavernosal nerve stimulation, determined that castrated rabbits had much lower pressures after stimulation than control rabbits did.  Notably, the pressures increased when castrated rabbits received exogenous testosterone replacement.
Causes contributing to erectile dysfunction can be broadly classified into two categories: organic and psychologic. In reality, while the majority of patients with erectile dysfunction are thought to demonstrate an organic component, psychological aspects of self-confidence, anxiety, and partner communication and conflict are often important contributing factors.
Let’s admit that not “talking about anything that could possibly be uncomfortable” is a sure-fire recipe for total disaster. Maybe you’re exaggerating, but if he can’t deal with anything even slightly difficult, then that is a bigger problem than pillow talk. Think about how exactly it would affect everything else in your relationship. He can’t choose not to deal. When good things are happening, it’s a shame he can’t say "I love you0". But when hard things happen, he can’t just say: "Um, pass."
The most important organic causes of impotence are cardiovascular disease and diabetes, neurological problems (for example, trauma from prostatectomy surgery), hormonal insufficiencies (hypogonadism) and drug side effects. Psychological impotence is where erection or penetration fails due to thoughts or feelings (psychological reasons) rather than physical impossibility; this is somewhat less frequent but can often be helped. In psychological impotence, there is a strong response to placebo treatment.
Studies to further define vasculogenic disorders include pharmacologic duplex grey scale/color ultrasonography, pharmacologic dynamic infusion cavernosometry/ cavernosography, and pharmacologic pelvic/penile angiography. Cavernosometry, duplex ultrasonography, and angiography performed either alone or in conjunction with intracavernous pharmacologic injection of vasodilator agents rely on complete arterial and cavernosal smooth muscle relaxation to evaluate arterial and veno-occlusive function. The clinical effectiveness of these invasive studies is severely limited by several factors, including the lack of normative data, operator dependence, variable interpretation of results, and poor predictability of therapeutic outcomes of arterial and venous surgery. At the present time these studies might best be done in referral centers with specific expertise and interest in investigation of the vascular aspects of erectile dysfunction. Further clinical research is necessary to standardize methodology and interpretation, to obtain control data on normals (as stratified according to age), and to define what constitutes normality in order to assess the value of these tests in their diagnostic accuracy and in their ability to predict treatment outcome in men with erectile dysfunction.
But if the blood flow is weak here, it is highly likely that it is also weak in arteries supplying the heart, raising the risk of a heart attack. In fact, some studies suggest that women with heart disease may also suffer sexual dysfunction: the clitoris, like the penis, is a vascular organ, and also relies on healthy blood flow for successful orgasms.
The link between chronic disease and ED is most striking for diabetes. Men who have diabetes are two to three times more likely to have erectile dysfunction than men who do not have diabetes. Among men with erectile dysfunction, those with diabetes may experience the problem as much as 10 to 15 years earlier than men without diabetes. Yet evidence shows that good blood sugar control can minimize this risk. Other conditions that may cause ED include cardiovascular disease, atherosclerosis (hardening of the arteries), kidney disease, and multiple sclerosis. These illnesses can impair blood flow or nerve impulses throughout the body.