Houston: Former Polish President Lech Walesa "spent himself in the fight against communism" and believes his heart is now paying the price.

He is currently receiving treatment in a Houston hospital .

"I worked a lot. I had a lot of stress. Communism cost me a lot. Now it's coming out," said Walesa, 64, sitting in pyjamas for an interview through an interpreter at Methodist Hospital, where he is being treated for a weak heart.

Walesa came to Houston on Monday for treatment after he developed shortness of breath and fatigue during a speaking trip in Mexico.

His cardiologist, Guillermo Torre, said tests show Walesa has cardiomyopathy, or a weakened heart, probably due to coronary artery disease and diabetes.

Walesa has been treated for the ailment before in Italy and Poland, but it has worsened, he said.

Torre said Walesa may need coronary bypass surgery or even a heart transplant, but doctors planned to implant a pacemaker first to see if the more drastic measures can be avoided or at least postponed.

White-haired and weary from medical tests, Walesa still flashed the charm and energy that inspired the Solidarity union in a 1980 strike that kicked off Poland's move to democracy and free markets.

His work earned him the Nobel Peace Prize in 1983 and a term as Poland's president from 1990 to 1995.

He still has strong opinions. He said the United States needs to regain the moral authority it had before the Iraq war began to erode US standing.

"What is missing is what it had during the Cold War, that moral and political leadership against evil," he said. "This is the part the US needs to build up, needs to emphasise, soft power," Walesa said.

In the US presidential race, he predicted the Democratic nominee, whether Barack Obama or Hillary Clinton, will defeat the expected Republican nominee, John McCain.