It was a House bill, amended by the Senate, and accepted by the House as amended.
Title: Patient Protection and Affordable Care Act
9/17/2009 Introduced in House
10/8/2009 Passed/agreed to in House: On motion to suspend the rules and pass the bill Agreed to by the Yeas and Nays: (2/3 required): 416 - 0 (Roll no. 768).
12/24/2009 Passed/agreed to in Senate: Passed Senate with an amendment and an amendment to the Title by Yea-Nay Vote. 60 - 39. Record Vote Number: 396.
3/21/2010 Resolving differences -- House actions: On motion that the House agree to the Senate amendments Agreed to by recorded vote: 219 - 212 (Roll no. 165).
3/21/2010 Cleared for White House.
If the House had amended it again, the Senate would have had to vote on it again.