But she said there will be some time to adapt and lessen the impact.
"Thirty-one million [patients] aren't going to walk in one day," said Heim.
Adding that many who do not currently have insurance are relatively healthy, she said, "We need to start doing the prevention to keep them [healthy]."
The American Medical Association estimates there are roughly 353,000 primary care doctors presently in the United States, which includes physicians in family medicine, internal medicine, general practice, pediatrics and obstetrics and gynecology.
In 10 years, the AMA estimates there will be a shortage of 85,000 doctors combined in primary care and specialties such as cardiology, oncology and general surgery.
While many have suggested an increasing role for physician's assistants and nurse practitioners, Heim and Pho both said they also tend to move into specialties rather than primary care because of the same incentives doctors have.
Another factor that needs to be examined further is how much care the newly insured will need.
"You have different subpopulations within that group of uninsured," said Keith Hennessey, who served as the senior White House economic advisor to President George W. Bush.
Hennessey, who has looked at the demographics of the uninsured in the past, noted that it includes some who are young and may not feel they need insurance, as well as some who may not be able to get health insurance because of a pre-existing condition. Just how many of each is unclear.
Grace-Marie Turner of the Galen Institute said approximately 16.7 million of the uninsured were people who wanted health insurance but could not afford it -- but some likely did not have a serious health condition.
"We're probably talking fewer than 10 million with pre-existing conditions," said Turner.
While many provisions of the health care bill will not kick in until 2014, $5 billion was set aside to create high risk pools in each state where people with pre-existing conditions who cannot otherwise be insured can get health insurance before the end of June.