Former U.S. Vice President Dick Cheney continues his recovery after undergoing heart transplant surgery March 24 at the age of 71. The vice president's operation has sparked a public debate over whether a person Cheney's age is too old to get a heart transplant. Age is only one factor when doctors consider who should get a new heart. Cheney has a history of heart problems. He had his first heart attack when he was only 37. He had four more over the course of three decades. His heart eventually became so diseased doctors replaced it with a mechanical heart pump about two years ago. Last year, he showed off the device to ABC News. "A little over a year ago I was at end-stage heart failure. My heart wasn't pumping enough blood to service my kidneys and my liver and so forth," Cheney said. Before a person can be eligible for a heart transplant, he or she must be diagnosed with end-stage heart disease. Dr. Samer Najjar, who oversees heart transplants at Medstar Washington Hospital Center, said a number of factors help doctors decide who gets a new heart. "We look at every other organ system in the body," he said. If those other organs are healthy, then doctors look at other factors. "We want to know what the patient's compliance is, what kind of social support do they have, are they going to be taking medications on a regular basis, will they follow instructions? These are critical in heart transplantation," said Najjar. At age 71, Cheney is among the oldest patients ever to get a new heart. "Age is one factor, a very important factor, but not the only factor," Najjar said. Najjar said older patients, in their mid-60s, have done well after a heart transplant. Almost 75 percent are still alive five years after the procedure and nearly half survive for 10 years after having a transplant. If an older person's other organs function well, doctors consider a patient's physiological age as a greater factor than chronological age. The United Network for Organ Sharing manages the national transplant system for the U.S. government. It reports that the number of donor hearts going to senior citizens has been steadily rising for more than 20 years.