CASTINE – EKG machines that map a heart’s rhythm may someday be as widespread as blood-pressure cuffs thanks to a new inexpensive, portable unit created by a husband-and-wife entrepreneurial team in this seaside town.

Jeffrey and Karen Siegel, Castine residents who are also on the local volunteer ambulance squad, won approval from the Food and Drug Administration in May to sell the EKG machine that’s about the size of a standard, hand-held cassette recorder. The unit, called ActiveECG, has three sensors that are stuck to a patient’s chest and a connection that plugs into any Palm Pilot, an off-the-shelf hand-held computer.

EKG results are displayed on the Palm Pilot, which also can store hundreds of electrocardiogram strips in memory. More importantly, the strips can be sent easily by computer or from Palm to Palm using the unit’s infrared beaming and synchronization functions.

“This product is revolutionary,” said Mark O’Keefe, a Dayton Beach, Fla., paramedic who reviews new products for the national EMT trade magazine called the Journal of Emergency Medical Services.

O’Keefe, who also sits on a state of Florida board that evaluates medical equipment, said EMTs are already overburdened with equipment. Having a hand-held unit instead of a behemoth 20-pound unit in tow is particularly useful for EMTs at events where they may be on bicycles or roaming on foot in a sports stadium, for instance.

“It’s amazing how small they’ve made it,” he said. Smaller is better, he said.

At just under $500, the device is also about six times cheaper than its bulkier competitors that sell for more than $3,000.

“This is the least-expensive EKG device on the market in the world,” Jeffrey Siegel declared proudly.

Some EKG units used by specialists in hospitals have more sensor leads and finer sensitivity than units of this sort that are designed as a quick assessment tool. And some of the bigger, 20-pound EKG units include defibrillator paddles used in attempts to snap a patient’s heart back into action.

But in the rough-and-tumble world of ambulance work, home health visits or backcountry medicine, this unit is tough and reliable, Jeffrey said.

ActiveECG is designed to withstand the shock of a defibrillator. The unit doesn’t require periodic manufacturer recalibration because it continually tests itself internally. The unit’s batteries last for six months under heavy use.

“Our unit is a down-and-dirty, keep-with-you workhorse that gives you immediate data when you need it,” Jeffrey Siegel said.

Although Siegel said this is the first such device that hooks to a Palm Pilot which has been approved by the FDA, there are ever more portable monitoring devices coming onto the market-particularly for people who want to monitor their own blood pressure and other health indicators. For now, ActiveECG cannot be purchased over the counter by people who aren’t in medicine although the developers hope that it might one day.

O’Keefe said the FDA approval differentiates medically tested products from others on the market. He said he’s found no flaws with the device as he prepares to write a Journal of Emergency Medical Services review.

Even in the vaguest terms the Siegels would discuss no financial issues including initial sales or projections. They said only that they are confident in their company and have spurned investment officers.

The Siegels aren’t first-time entrepreneurs. In Washington they grew a company that developed eight FDA-approved software programs to bridge diagnostic machines to PCs and Macintosh computers in hospitals. Then as now, Jeffrey Siegel would develop the ideas and technical approaches and Karen Siegel would test the ideas and handle FDA and marketing concerns. The eight initial products they developed are used now in about 2,000 hospitals, Jeffrey Siegel said. The couple sold that first company to Evergreen Technologies Inc. before moving to Maine.

At about that time the two realized they could successfully run their business outside a metropolitan environment. After all, most of their clients were in Japan and advancements in communication technology reduced distance issues, he said.

Still, the company relies heavily on contractual arrangements with companies outside Maine to carry out the production and sales of its products. A company in Ohio provides the sales technology and work force for Active Corp. The design and plastic work on ActiveECG were done in partnership with the Boston branch of Fitch, a company that does such work for many huge consumer companies. A New England testing firm was hired to put the device through its paces. Informally, some of the earliest test subjects were direct family members. When one older relative asked to be hooked up his rhythm raised questions. A doctor was consulted and the relative’s irregularity was diagnosed and treated, Jeffrey Siegel said.

Using its partnerships, Active is already getting ready for the launch of a product this fall that Jeffrey Siegel said will be “10 times” as important as ActiveECG.

Regardless of how well the products do, the Siegels said they love Castine and plan to stay. Washington was too big and impersonal, they said.

Once they came to Castine they immediately enrolled in a local EMT course.

“For us it was part of coming to a little community and making a difference,” Karen Siegel said. “In Washington you feel like you can’t make a difference.”

As the two describe their entrepreneurial and volunteer ambulance work, either inside their Main Street office or out on the street in front of an ambulance equipped with the old and new EKG machines, every other pedestrian or driver shouts a greeting or raises a hand with a smile.

“We’re competing against billion-dollar companies but we can compete here in Castine, Maine,” Jeffrey Siegel said as he looked out onto the street. Like many other businesspeople in Maine whose business extends beyond state borders, Siegel said one of his biggest location difficulties stems from inadequate airline schedules.

“I really wish there were better air travel,” he said. “To fly west from here is unbearable.”

What do townspeople think of the couple’s unusual business?

“We’re the quirky, high-tech people here,” Jeffrey Siegel said. “But we’ve been here for eight years now.”