#2 Physically exhausted. If you’ve been cranking it at the gym, haven’t been sleeping well, or you’ve been working your ass off at your job, getting tangled up with your lover for even more physically demanding activities may not sound ideal. Physical exhaustion has a direct effect on your ability to get aroused. The only fix for this one is to get some rest.
The nerves and endothelium of sinusoids and vessels in the penis produce and release transmitters and modulators that control the contractile state of corporal smooth muscles. Although the membrane receptors play an important role, downstream signaling pathways are also important. The RhoA–Rho kinase pathway is involved in the regulation of cavernosal smooth muscle contraction. 
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.
*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.
The term "impotence," as applied to the title of this conference, has traditionally been used to signify the inability of the male to attain and maintain erection of the penis sufficient to permit satisfactory sexual intercourse. However, this use has often led to confusing and uninterpretable results in both clinical and basic science investigations. This, together with its pejorative implications, suggests that the more precise term "erectile dysfunction" be used instead to signify an inability of the male to achieve an erect penis as part of the overall multifaceted process of male sexual function.
Pills such as Viagra® are the most common ED treatment, but they don’t work for everyone. Some guys find they cause bothersome headaches or persistent stomach troubles. Some have serious side effects such as chest pain and vision or hearing changes. Others don’t respond to the medication at all. And still others don’t like having to wait for the pill to take effect.