The House of Representatives narrowly passed the American Health Care Act on Thursday, the Republicans’ first successful attempt in seven years to repeal and replace the Affordable Care Act, President Obama’s signature health care law.

An updated version of the bill had not yet received a score from the nonpartisan Congressional Budget Office on Thursday afternoon, so it was unclear exactly how many individuals would lose health insurance coverage under the American Health Care Act as it exists. A CBO analysis of an earlier version put forward by the House in March indicated 24 million people would lose coverage.

Patients with pre-existing conditions like heart disease and stroke could fare poorly under the AHCA. Under the bill, states would be permitted a waiver that, under certain circumstances, gives  the ability to waive health status rating protections. Weakening these rules could enable insurers to charge patients with pre-existing conditions higher prices for the same services.

States that waive health status rating protections would be required to set up a high-risk sharing program, which may include a high-risk pool. Such pools often lead to higher premiums, long waits and inadequate coverage.

Republican Rep. Fred Upton of Michigan on Wednesday introduced an amendment that would provide an additional $8 billion over five years to help patients pay out-of-pocket costs or potentially higher premiums. However, the proposal does not specify who would be eligible for assistance; how much of their costs would be covered; or how much they would be required to pay out-of-pocket for their premiums.

Eight patient groups, including the American Heart Association, said the amendment is not adequate  for the 129 million Americans with pre-existing conditions.

“There is no substitute for fundamental, unequivocal protections for people with pre-existing conditions,” the groups said in a joint statement.

In addition, the AHCA bill as issued would allow states to waive the requirement of essential health benefits. Under the ACA, states are required to cover 10 essential health benefits, such as preventive and wellness services, chronic disease management and rehabilitative care. Eliminating these requirements would threaten access to preventive and other clinical services that are critical in helping prevent and manage cardiovascular diseases.

The bill would also shift billions in costs to states by making drastic cuts to the Medicaid program. It is unlikely that they would be able to meet their increased financial obligations under this plan.

AHA Chief Executive Nancy Brown expressed disappointment at House members who “failed to stand up for America’s patients.”

She called on the Senate to “take a more thoughtful approach to our nation’s health care system and remember that American lives hang in the balance. “

The bill now heads to the Senate, where it is likely to undergo significant changes.