The 51-year-old Heck was seeking a second term Tuesday against Oceguera, a 44-year-old former North Las Vegas firefighter and Democratic state Assembly speaker.
Much of the campaign centered on an Oceguera ad that Heck argued falsely portrayed him as supporting a bill that would ban abortion for rape victims.
Heck says taxpayer money shouldn't fund abortions.
But the congressional measure specifically exempted pregnancies resulting from rape or incest, and the law didn't pass.
Oceguera continued to stand behind the ad.
The 3rd District around Las Vegas is extremely competitive.
Democrats hold a slight voter registration edge, but a large number of voters in the district call themselves nonpartisan.