Wayne Schneider's heart stopped beating late last year while the Minneapolis paramedic was out on an emergency call. Another medic performed CPR for a few minutes, and then used a medical device that delivered cardiac compressions mechanically for 64 minutes, until Mr. Schneider's heart started beating normally on its own. "I'm not sure people would have been able to sustain manual CPR for so long," said Mr. Schneider, 57. "I'm a lucky guy." He may have been luckier than he knows. Though widely available, the machine used to keep him alive, called an external cardiac compressor, was never subjected to the rigorous premarket approval process that the Food and Drug Administration routinely requires for new drugs.