HAlthough she has to fight in an encouraging turnout, and the Republicans rely on white country voters to support Mr Heller.
Latest polls for Nevada close at 22:00 EST (03:00 GMT).
Senator Heidi Heitkamp, re-elected in 2016 in a state that won nearly 40 points in 2016, is considered the most vulnerable Democrat in the Senate.
Ms. Heitkamp is pressured by conservative voters when she votes against the candidacy of the Brett Kavanaugh Supreme Court, as she proposed. However, Ms. Heitkamp announced her first support last year to Mr. Trump's first Supreme Court judge, Neil Gorsuch.
Their opponent, Kevin Crammer, also has the support of the president. Mr. Trump launched a Republican fundraiser in early September, which raised more than $ 1 million in donations for his campaign.
Latest polls for North Dakota close at 23:00 EST (4:00 GMT).
The race between Democratic Senator Bill Nelson and his Republican challenger Rick Scott is one of the most expensive of the year. Mr. Scott, Florida's Governor, has challenged Mr. Nelson's papers in Washington and distanced himself from the President to avoid losing Puerto Rican voters.
Republicans see the seat as one of their most promising opportunities to gain an extra seat in the Senate, and have spent much in the race. Surveys show the two almost around the neck – an interesting race for the election night.