Republican Rep. Joe Heck on Monday entered the race for the U.S. Senate seat being vacated by Nevada Democrat Harry Reid, setting in motion what could be one of the top Senate races of 2016.

Heck made the announcement in a video posted online, citing his background as a medical doctor in the emergency room and on a military deployment to Iraq. He talked about the struggles his family endured growing up and having the help of a union and social services when his father was out of work.

"When my father needed emergency surgery, Medicare covered it. That's why I'll protect Medicare and Social Security and preserve it for future generations," Heck said in the three-minute video on his website.

The Republican congressman will likely face off against Reid's hand-picked successor, former state Attorney General Catherine Cortez Masto. The Democrat announced her candidacy in April and saw one potential primary foe -- U.S. Rep. Dina Titus -- decide against running in favor of seeking re-election to the House.

Lieutenant Gov. Mark Hutchison, former Assemblywoman Heidi Gansert, Las Vegas City Councilman Bob Beers and former Lieutenant Gov. Brian Krolicki -- all Republicans -- also have decided against running, clearing the way for Heck.

Popular Republican Gov. Brian Sandoval announced last month that he wouldn't seek the seat held by the 75-year-old Reid. Sandoval said he wanted to focus on improving the state's infrastructure and higher education system rather than embarking on a demanding campaign.

Reid, the Senate Democratic leader, announced in March that he would not seek a sixth term and immediately backed Cortez Masto. The decision came after an exercise injury left Reid blind in one eye.

Heck served in the state Senate between 2004 and 2008 and won the congressional seat in 2010 after defeating Titus by less than 2,000 votes.

He won re-election by big margins in 2012 and 2014, even though Democrats have a slight edge in voter registration in the district.

Heck has spent more than two decades as an Army reservist, including three active-duty tours and a deployment in Iraq. He's also the only one-star general in Congress.

Heck was born in New York and moved to Nevada in 1992. He lives in Henderson with his wife, Lisa, and three children.