The heart monitor leader iRhythm Holdings is moving to help doctors track their patients' health outside the clinic.

iRhythm is acquiring its small rival VitalConnect for $287.5 million -- $237.5 million in cash and $50 million in stock .

With the deal, announced Thursday, comes VitalConnect's patient-monitoring products, which give doctors a live look at a patient's vitals while the patient is going about their life -- for up to a month at a time.

iRhythm's Zio monitor patch is up for Food and Drug Administration approval on some of these capabilities, but VitalConnect's VitalPatch already has it.

During iRhythm's earnings call, also on Thursday, CEO Quentin Blackford told analysts that the deal will expand his company's sales opportunity.

"Having VitalPatch in there gives us access to the entire market, which is probably $1 billion market, growing in high single digits," said Blackford. "It's a probably incremental $500 million market opportunity for us."

Both companies sell patch monitors that look for errant heart rhythms, such as atrial fibrillation, that can lead to strokes when untreated. The VitalPatch also can track nearly a dozen other vital signs, like respiration and body temperature.

Healthcare innovators have been making slow progress at connecting wearable monitors with medical information systems, as Barron's has reported.

From Apple Watches to glucose sensors, these gadgets could allow doctors to catch problems before they send people to the emergency room, or track patients after they have been released from the hospital.

Medical devices necessarily need careful regulation, but the federal government has task forces working to allow some medical use of information from health gadgets like the Oura ring or the Whoop fitness band.

For now, remote medical monitoring remains the province of FDA-approved devices like iRhythm's Zio.

Blackford told listeners that iRhythms early-pilot programs with its products have shown 85% accuracy in finding people with arrhythmias before they were diagnosed.

Meanwhile, iRhythm's core business of heart rhythm monitoring keeps growing. Sales increased 20% in the June quarter, to $224 million. Earnings were $19 million, or 58 cents a share, adjusting away charges like stock compensation and legal expenses.

The company raised guidance for the year, expecting sales will grow about 18%, to at least $880 million.

iRhythm stock opened Friday at around $131, up 7% from Thursday's opening price, then eased back in afternoon trading to $128.