Masto tied Heck at 37 percent in the Suffolk University poll of likely Nevada general election voters. Third party candidates Tony Gumina, Tom Jones and Tom Sawyer all polled at 1 percent, and Jarrod Williams polled at 0 percent.
Suffolk University has not polled Nevada likely voters on the Senate election previously, but a recent CBS/YouGov poll showed Heck ahead by three percent, 38-35, earlier this month.
The poll was conducted Aug. 15-17 over the phone among 500 likely Nevada voters, and has a margin of error of plus or minus 4.4 percent.
TPM's PollTracker Average of the Nevada Senate race shows Heck ahead of Masto, 37.3 to 36.3.