According to studies, having a dog as a companion could add years to your life. One study concluded that owning a dog played a significant role on survival rates in heart attack victims. In another one of these studies, patients were evaluated for one year after they had been admitted to the hospital. It was discovered by Researchers that the patients who were alive one year after having a heart attack were more likely to own a dog.
In terms of determining the patient's likelihood of long-term survival, another study that focused on the top psychological factors that contributed to the recovery of patients with heart-disease, ranked pet ownership on top. Studies have also shown dogs can have a soothing influence that in turn helps to keep blood pressure levels in a healthy range. 
Dr Deborah Wells a psychologist from Queen's University, Belfast, writing in the British Journal of Health Psychology said dog owners tended to have lower blood pressure and cholesterol. After reviewing dozens of earlier research papers which explored the health benefits of pet ownership she confirmed that pet owners tended in general to be healthier than the average member of the population.
However, her research suggested that dog ownership produced more positive influence than cat ownership. As well as lower blood pressure and cholesterol, she said dog-owners suffered fewer minor ailments and serious medical problems. There was also the suggestion that dogs could aid recovery from serious illnesses such as heart attacks, and act as 'early warning' to detect an approaching epileptic seizure. 
In fact, the State University of New York at Buffalo conducted a study which involved 24 stockbrokers that were taking prescription medication for high blood pressure. Researchers determined that adding a dog or cat to the stock brokers' lives helped stabilize and even reduce their levels of stress.
In other research conducted by the University of Missouri-Columbia studies suggested that there are hormonal changes that occur when humans and dogs interact which could help people cope with depression and certain stress-related disorders. Apparently the simple act of taking a few minutes to pet your dog prompts a release of a number of "feel good" hormones in humans, including serotonin, prolactin and oxytocin.
Other studies showed that the presence of animals, especially dogs, helped to reduce the anxiety of people confronting stressful situations, such as dental surgery. Separate studies reported that walking a dog can not only contribute to a person's weight loss but can also be a catalyst for interaction with other people, which can help improve a person's sense of well-being.
Most studies show therapy using dogs to be one of the most cost-effective methods of helping people suffering from emotional challenges and state that people living without pets are exposed to "more persistent fears, increased feelings of panic, experience more frequent headaches and take more medication for stress-induced illnesses than pet owners ".
In fact the Siskin Hospital in Tennessee has a "Pet Therapy" program to assist in rehabilitation. They state: "The Pet Therapy Program uses carefully screened dogs and cats as an integral part of physical, speech, recreational and occupational therapies to address treatment goals including improving range of motion, strength and endurance, balance, mobility, and sensation. In addition to the physical benefits of pet therapy, patients form a connection with the animal; reducing stress and building self-esteem through the animals' unconditional acceptance ". 
So next time you start feeling stressed out or overwhelmed go spend some time with your dog and if you do not have a dog you may want to consider getting one. Maybe you can get your doctor to prescribe a dog for you and get your health insurance to pay for it. Just kidding.