Mary Wusterbarth thought her toddler was struggling with an ear infection when she seemed sluggish. Instead, a virus had attacked the little girl's heart, damaging it beyond repair. Brea needed a transplant.

Within three weeks of a 2007 doctor visit, the 20-month-old had exhausted the $1 million lifetime maximum on her health insurance. Her parents have scrambled ever since for ways to cover thousands of dollars in monthly medical costs.

"We have no idea what kind of financial future we have," said Wusterbarth, of Wake Forest, N.C. "The medical bills come almost daily. There's never an end."

Insurers set lifetime limits to keep rates low on some policies, but holders are learning that individual caps that seemed large quickly max out as health-care costs soar. Several patient-advocacy groups are prodding insurers to raise the caps, which generally don't adjust for inflation. Congress also is considering two bills that would do that.

Only 1 percent of employer-offered group plans — the largest health-insurance segment — had caps as low as $1 million last year, according to a survey by The Henry J. Kaiser Family Foundation. But 22 percent had caps of less than $2 million, and some want to see all these relatively low maximums eliminated.

Insurers, however, say most health coverage already offers either a comfortable maximum of several million dollars or unlimited coverage. They note that more government regulation could lead to higher coverage costs, and low lifetime caps help them offer a greater variety of coverages.

"I think the discussion needs to move into why do some health-care services cost hundreds of thousands of dollars and what can we do to address those issues," said Robert Zirkelbach of America's Health Insurance Plans, a trade association representing nearly 1,300 insurers.

Kelly and Tom Treinen used to think the $1 million individual cap that came with the insurance they had for seven years offered plenty of protection. In fact, they chose that plan, which Kelly received through her job as an elementary school principal, over a higher-priced option through Tom's business. That one offered a $5 million cap.

Then doctors diagnosed their teenage son, Michael, with an aggressive form of leukemia in May 2007. His treatment called for 10 doses of a chemotherapy drug that cost $10,000 per dose. A 56-day stay in an intensive care unit cost about $400,000.

Michael reached his $1 million lifetime maximum in less than a year. The Noblesville, Ind., family had to issue a public plea for help after a hospital told them it needed either $600,000 in certified insurance or a $500,000 deposit to continue preparing for a critical bone marrow transplant.