Severe pain, vision problems, nausea and sensitivity to light are all symptoms of a migraine headache.

Research into why migraines happen is leading doctors to examine not a patient's head but his or her heart. They're looking to prove that many migraines are caused by a very common, often undiagnosed heart defect.

Damon Cable is a very busy pediatric nurse practitioner.

When Cable's migraines hit, on an average of twice a week, working is not easy.

"When they're really bad you can't do anything. You can't tolerate bright lights, you can't tolerate noises, you can't tolerate children, you just have to go to a dark room and lie down,” said Cable.

Frustrated, Cable turned to Mayo Clinic where doctors told him that his migraines might be caused by a tiny hole in his heart, called a Patent Foramen Ovale.

"Patients with migraine headache are much more likely to have a PFO than the general population," said Mayo Clinic Dr. Bart Demaerschalk.

Dr. Demaerschalk teamed up with colleague Tiffany Koch to study whether or not closing PFOs reduce the frequency and severity of migraines. A PFO is a hole between two chambers, or atria of the heart. Doctors said usually these holes close soon after birth, but for one-fourth to one-fifth of the population they stay open.

The hole allows blood that's normally filtered in the lungs to bypass the lungs and move between the chambers of the heart. The theory is that unfiltered blood may carry tiny clots or chemicals to the brain and cause migraines. In the study, half of the people undergo a catheterization procedure to close the hole. Half undergo a sham procedure. If the first group ends up with fewer headaches, study results will be positive. Cable is positive his PFO is closed.