When Melissa McCann (left) suffered a stroke in 2007, her twin sister, Terry Blanchard, helped her make a full recovery. McCann is now back to work as a flight nurse with Life Flight at the Eastern Maine Medical Center in Bangor. David Wright/Redux Pictures for NPR hide caption

itoggle caption David Wright/Redux Pictures for NPR

Students at the College of Central Florida in Ocala, Fla., perform CPR on a mock patient. Bruce Ackerman/Ocala Star-Banner /Landov hide caption

itoggle caption Bruce Ackerman/Ocala Star-Banner /Landov

A 3-D reconstruction of Mummy 38's CT scans shows calcification in her aorta and iliac arteries. Courtesy of The Lancet hide caption

itoggle caption Courtesy of The Lancet

ATLANTIC CITY, NJ - JULY 8: The roulette wheel spins at Caesars Atlantic City July 8, 2006 in Atlantic City, New Jersey. Caesars, along with Atlantic City's 11 other casinos reopend this morning after they were forced to close their gambling floors for the first time in their 28-year history due to the New Jersey state budget impasse. (Photo by William Thomas Cain/Getty Images) William Thomas Cain/Getty Images hide caption

itoggle caption William Thomas Cain/Getty Images

An angiogram of a 48-year- old patient after treatment for a stroke. A blockage was targeted with clot-busting drugs using a catheter. Zephyr/Science Source hide caption

itoggle caption Zephyr/Science Source

Maribel Ramos, 13, has both sickle cell disease and an abnormality of blood vessels called moyamoya. Both put her at risk of stroke, and, together, they add up to a 95 percent chance of a major stroke. Richard Knox/NPR hide caption

itoggle caption Richard Knox/NPR

Before filling one of these tubes with blood for a cholesterol test, you're supposed to keep your stomach empty. But that may not be necessary. Nancy Louie/iStockphoto.com hide caption

itoggle caption Nancy Louie/iStockphoto.com

This gentleman may want to have a chat with his cardiologist. Bill Losh/Getty Creative Images hide caption

itoggle caption Bill Losh/Getty Creative Images