It was the former vice-president's fifth heart attack since 1978 and the latest in a long list of health scares for him.
Cheney was admitted to George Washington Hospital on Monday after experiencing chest pains, Long said.
Cheney, who suffered his first heart attack when he was 37, has had quadruple bypass surgery and two artery-clearing angioplasties.
Despite his persistent health problems, Cheney's time in office saw him emerge as one of the country's most powerful vice presidents and a champion of the Republican right wing wielding massive behind-the-scenes influence in the Bush administration.
Since leaving the White House, Cheney has kept a high profile, repeatedly attacking the current administration of Barack Obama accusing him of being alarmingly naive on national security.
He has also been a vocal critic of Obama's plans to close the US detention facility at Guantanamo Bay, Cuba, and hold the trials of several high profile detainees in civilian courts rather than military tribunals.
Fitted with pacemaker
Cheney's most recent heart attack was shortly after the November 2000 election that saw him elected as vice-president.
However, it was described as mild and he was subsequently fitted with a pacemaker to regulate his heart rhythm.
The device was replaced in 2007 after its battery wore down, according to his office.
In 2008, doctors restored a normal rhythm to his heart with an electric shock, the second time in a year.
Among his extensive government service, working in four different presidential administrations, Cheney served as US defence secretary between 1989 and 1993 under the presidency of George Bush Sr.