That's when someone's breathing is interrupted during their sleep.
If you know someone with heart failure, they could also have "central sleep apnea." A third of those with heart failure have it.
Unlike other sleep apnea types, people with central sleep apnea typically don't snore.
But the brain isn't sending the right signals to keep someone breathing while they sleep. It can be very dangerous, and there haven't been good treatments for it.
Now, there may be a new remedy.
Leslie McGuire says he used to wake up at night gasping for air.
McGuire recalls, "It scares you when you wake up and you go oh my God what's happening."
He has central sleep apnea. A standard C-Pap breathing machine usually won't work.
But it seems a new device called 'remede' (as in 'remedy') is working.
In a test, doctors at 11 hospitals worldwide implanted this pacemaker-like device in 47 patients.
It goes under the collarbone, and a wire runs to the diaphragm.
At night, it signals the diaphragm to breathe.
It cut episodes of not breathing by 80 per cent, and it eased daytime sleepiness.
Dr. William Abraham, the lead researcher at the Ohio State Wexner Medical Center, says, "The beauty of the 'remede' device is that it requires no patient adherence. It's implanted, it's turned on, it's automatic."
Dr. Abraham presented his results at today's session of the 17th annual meeting of the Heart Failure Society of America.
A second round of tests is underway, and is expanding to 25 medical centers.
McGuire says he is happy he was in the first trials - the difference for him was remarkable.
"I wake up now, I've got the energy to get up. I get up and move around - it's just a hundred per cent different," he says.
Most people have obstructive sleep apnea, not central sleep apnea. Snoring is less common with the central type.
However, many other symptoms are similar, such as: abrupt wakening during the night, abnormal breathing, daytime sleepiness, headaches, and difficulty concentrating.
These conditions can lead to many other health problems. If you have any of those symptoms, talk to your healthcare provider about being tested.
The American College of Physicians today issued new recommendations for people with obstructive sleep apnea.
They say patients should lose weight and use continuous positive airway pressure (CPAP) for their first therapy.
"The evidence indicates that intensive weight loss interventions help improve sleep study results and symptoms of OSA," said Dr. Molly Cooke, president of the College of Physicians.
ACP recommends a mandibular advancement device (MAD) as an alternative therapy for patients who prefer it or who can't handle CPAP treatment.
The evidence shows that the incidence of OSA is rising, likely because of the increasing rates of obesity.