WASHINGTON (CNN) -- Rep. Nick Lampson underwent quadruple bypass surgery Sunday, after doctors in Washington noticed irregularities and urged him to seek further consultation with his physicians in Texas.

Lampson spokesman Bobby Zafarnia tells CNN that doctors expect the Texas Democrat to make a full recovery, although he will not return to Capitol Hill for another three to four weeks as he recuperates.

"He is doing well," Zafarnia said. "Everything is going as doctors had predicted. I spoke with the physicians this morning, and they were very optimistic about everything including the recovery and how he is doing today. They expect him to make a full recovery."

Doctors with the Houston-based Texas Heart Institute at St. Luke's Episcopal Hospital in the Texas Medical Center performed the surgery.

Lampson had served in the House from Jan. 1997 until losing reelection in 2004 but then made national headlines in the 2006 election cycle when he challenged then-Rep. Tom DeLay, R-Texas. The embattled former House Majority Leader at the time was fighting charges that he broke state campaign finance laws, and was also under scrutiny for his close association with disgraced lobbyist Jack Abramoff. DeLay eventually resigned from Congress, but legal challenges blocked Republicans from replacing him on the ballot. Lampson's victory was one of many that helped Democrats wrest back control of the House from Republicans in the 2006 elections.