(CNN) - House Majority PAC, a group that supports Democratic efforts to take control of the House of Representatives, raised $7.5 million in 2013 as it gears up for this year's midterm elections, a spokesman said.
The amount is more than double the $3 million it raised in 2011, the off-year for the 2012 election cycle.
Andy Stone, the super PAC's communications director, said the group is working to combat the efforts of billionaires Charles and David Koch, better known as the Koch Brothers.
The conservative duo has been focused on targeting Obamacare and candidates who support it, trying to make the health care law the dominant issue of the 2014 midterm elections.
Americans for Prosperity, a group backed by the Koch Brothers, spent $16 million on television ads in the fall, including millions specifically against vulnerable House Democrats in recent months.
But Stone said Democrats are stepping it up this year, as well.
"Fortunately, as they witness a House GOP seemingly allergic to creating jobs or getting anything done, Democrats are both responding in a big way and recognize the continuing need to be aggressive," Stone said.
So far this cycle, House Majority PAC has already run television ads in six races (WV-03, FL-02, IL-13, NV-03, OH-14, CO-06) and radio ads in a seventh race (MN-02).
The group has also announced plans to run television ads in Tucson and Phoenix to match attack ads against Democratic Reps. Ron Barber and Ann Kirkpatrick by Americans for Property.
Democrats need to pick up 17 House seats to regain control of the House, something most political analysts say is now out of their reach due to the low number of competitive races.
In the 2012 cycle, Democrats gained a net of eight seats in the House. House Majority PAC spent $36 million in 52 races.
CNN Political Editor Paul Steinhauser contributed to this report.
From CNN on January 14, 2014.