American Mardy Fish was forced to pull out of the U.S. Open for "health reasons" on Monday afternoon. Fish's withdrawal means that his opponent, top-ranked Roger Federer, moves on to the quarterfinals. There was no specific reason given for Fish's exit from the tournament other than that it was health-related.

According to a Yahoo! Sports report, Fish had heart problems earleir this year, was hospitalized for an elevated heart rate following an event in Miami and then underwent a procedure to attempt to correct his heart issues.

Federer, who has now reached 38 consecutive quarterfinals in Grand Slam tournaments, will go up against No. 6 Tomas Berdych who advanced with a 7-4, 6-4, 6-1 win over No. 11 Nicolas Almagro on Monday.

The only other completed match was No. 12 Ana Ivanovic easily beating Tsvetana Pironkova 6-0, 6-4 this morning.

No. 4 Serena Williams is currently on the court at Arthur Ashe Stadium, leading Andrea Hlavackova two games to none in the second set after winning the first set 6-0.

For more on the 2012 U.S. Open, check out SB Nation's tennis hub. Head over to the official U.S. Open website for live scores.