According to MLB.com's Joe Frisaro, the Nationals acquired recently-designated reliever Logan Kensing from the Marlins for minor league reliever Kyle Gunderson. Gunderson was drafted out of Rice in '07.
Kensing, 26, was designated for assignment by Florida after just 7.3 innings this year. Last year, he logged 55.3 innings with a 4.23 ERA, struggling with his control. He had Tommy John surgery in August of 2006.