Preliminary ratings are in for the one and only Vice Presidential debate. At least 43 million tuned in to the three cable networks Fox News, MSNBC and CNN as well as CBS, ABC and NBC. That number will go up when final numbers are released and will include additional networks like PBS, FOX, Univision and the business channels.

• Update: Final Ratings: 51.4 Million Watch

Fox News is the most watched network with 10 million viewers, more than MSNBC (4.38 million) and CNN (4.15 million) combined.

For the broadcasters, according to Nielsen Fast National data, CBS was the most watched, followed by ABC then NBC, with less than 500,000 viewers separating the big 3 networks.

(As we saw with the first presidential debate  — watched by 67.2 million viewers — preliminarily Fox News was the most watched, but when finals came out ABC was on top.)

It’s unlikely last night’s debate between Vice President Joe Biden and Rep. Paul Ryan will get close to the numbers of the Biden-Sarah Palin face-off four years ago. 69.9 million viewers tuned in that night — tied with a Bush-Clinton-Perot debate in 1992 for the second most-watched debate ever.

• Cable News 9:00-10:30PM:

FNC: 10,019,827 in total viewers (3,057,099 in 25-54)
MSNBC: 4,378,671 in total viewers (1,619,542 in 25-54)
CNN: 4,145,951 in total viewers (1,523,882 in 25-54)

• Broadcast Fast Nationals 9-10:30PM:

CBS: 8,308,421 in P2+ (3,400,620)
ABC: 8,287,610 in P2+ (2,995,352)
NBC: 7,851,757 in P2+ (3,560,307)

• Broadcast Post-Debate Analysis 10:33-11:00PM:

NBC: 6,697,000 in P2+ (2,875,000 in 25-54)
ABC: 6,057,000 in P2+ (2,372,000 in 25-54)
CBS: 5,931,000 in P2+ (2,187,000 in 25-54)

• 8:00-11:00PM (cable news primetime)

FNC: 8,052,332 in total viewers (2,283,719 in 25-54)
MSNBC: 3,516,671 in total viewers (1,275,399 in 25-54)
CNN: 3,265,598 in total viewers (1,164,117 in 25-54)

Four years ago, Fox News broke a record when it drew 11.1 million viewers for the Biden-Palin debate, its most-watched program ever.