Erectile dysfunction is now a recognized marker for cardiovascular disease as a result of several studies. The artery size hypothesis has been used to explain how ED acts as a silent marker of vascular disease elsewhere in the body, and more significantly as a marker of CAD.

Artery size varies considerably according to location within the vascular system.

For example, the lumen of the penile arteries is considerably smaller (1–2 mm) compared with that of the coronary (3–4 mm), carotid (5–6 mm), and femoral (6–8 mm) arteries. Because of their smaller size, the same level of plaque burden and/or endothelial dysfunction has a greater effect on blood flow through the penile arteries than through the coronary, carotid, and femoral arteries. Therefore the clinical manifestations of penile endothelial dysfunction (ED) may become evident before the consequences of coronary or peripheral vascular disease. By the time the lumen of the larger arteries become significantly obstructed (>50%), the penile blood flow may have already decreased considerably, which explains why so many men with CAD have ED.

Thus on the basis of artery size hypothesis and the fact that the endothelium is the same throughout the arterial tree, a malfunction in the penile arteries causing ED may be a predictor of silent subclinical cardiovascular disease (CVD). Furthermore, because an acute coronary syndrome often arises as the result of the rupture of a subclinical plaque, the presence of ED may also be an early warning sign of an acute event as well as being a manifestation of advanced obstructive CAD.

In 1999, Pritzker presented a preliminary report entitled “The penile stress test: A window to the hearts of man”. He reviewed the results of exercise stress testing, risk factor profiles, and, in selected cases, angiography in 50 men with ED, who had no cardiac symptoms or past history. Multiple cardiovascular risk factors were present in 80%. Exercise tests positive for ischemia were found in 28 of the 50 men. Coronary angiography was performed in 20 men and revealed left main stem or severe three-vessel disease in 6 men, moderate two-vessel disease in 7 men, and significant single-vessel disease in 7 men. This study identi-fied the significant incidence of occult coronary disease in cardiologically asymptomatic men presenting with ED to a urological service. Others have reported similar findings and noted the occurrence of ED before cardiac symptoms developed. In a study comparing the velocity of cavernosal artery blood flow with the presence of ischemic heart disease in men with ED, a low peak systolic velocity (PSV) predicted the presence of CAD. A PSV below 35 cm/s was associated with CAD in 41.9% of men and above 35 cm/s in only 3.7% of men.

In support of this concept, a series of 300 patients with acute chest pain and angiographically proven CAD were evaluated with a semi-structured interview to assess their medical and sexual histories prior to presentation. The prevalence of ED among these patients was 49% (n = 147). In these 147 men with both ED and CAD, ED was experienced before CAD symptoms in 99 patients (67%). The mean time interval between the occurrence of ED and the occurrence of CAD was 38.8 months (range: 1–168 months). Interestingly, all men with ED and type 1 diabetes developed sexual dysfunction before the onset of CAD symptoms. The authors do point out the absence of a control group with CAD and normal erections, but their findings clearly identify the need to assess cardiovascular risk in all males presenting with ED without obvious psychosexual etiology, especially in patients with diabetes.