Doctors treating Teresa Heinz Kerry have ruled out several possible causes that led to her hospitalization over the weekend, including heart attack, stroke or a brain tumor, a family spokesman said.

Heinz Kerry was hospitalized with seizurelike symptoms on Sunday while vacationing in her Nantucket home with Secretary of State John Kerry.

She remains in "fair" condition at Massachusetts General Hospital in Boston, after being transferred there from a Nantucket hospital late Sunday.

With his wife now stable and "improving," Kerry returned to Washington today to participate in the U.S.-China Strategic Economic Dialogue, spokesman Glen Johnson said.

"The family does not anticipate making any further statements until Mrs. Heinz Kerry is discharged from the hospital," Johnson said.

State Department spokeswoman Jen Psaki told reporters that though the secretary plans to attend as much of the U.S.-China meeting as he can, his schedule will remain flexible. Psaki said that Deputy Secretary of State Bill Burns will attend any events in Kerry's stead should he need to return to Boston before Thursday, when the meeting ends.