Apple has listed products it says should be kept a "safe distance" away from medical devices like pacemakers and implanted defibrillators.
The list includes iPhone 12 models, Apple Watch and MacBook Pro.
Many consumer-electronic devices contain components, such as magnets, which can interfere with medical devices.
The BBC has asked for comment from Apple, which has promoted heart health as a feature of its products.
Some Apple Watches can take an electrocardiogram test that records the timing and strength of the electrical signals that make the heart beat.
But the current notice warns of risks from components in some products.
"Under certain conditions, magnets and electromagnetic fields might interfere with medical devices," Apple wrote.
For example, it noted, "implanted pacemakers and defibrillators might contain sensors that respond to magnets and radios when in close contact".
Implanted defibrillators send electrical pulses to regulate abnormal heart rhythms.
The firm said the listed products should be kept more than 15cm (6in) away from medical devices, double that if they are wirelessly charging.
The new list was published on a support page, that earlier this month had said, iPhone 12 models were "not expected to pose a greater risk of magnetic interference to medical devices" than other iPhones.
But the website MacRumours, which first noted the list, highlighted research suggesting that the iPhone 12 could interfere with implanted devices.
Research published in the Journal of the American Heart Association found that "Apple's iPhone 12 Pro Max MagSafe technology can cause magnet interference", and consequently had the potential "to inhibit life-saving therapy".
MagSafe enables fast wireless charging.
While researchers acknowledged the small scale of the study, lead investigator Dr Michael Wu wrote in a press release that they were surprised by the strength of the magnets in the iPhone 12,
"In general, a magnet can change a pacemaker's timing or deactivate a defibrillator's life-saving functions, and this research indicates the urgency for everyone to be aware that electronic devices with magnets can interfere with cardiac implantable electronic devices."
Marie Moe, a computer security consultant for Mnemonic, who has a pacemaker herself and studies their technology, told the BBC she was not worried.
"These Apple gadgets are generally not emitting large magnetic fields, unlike heavy machinery, big concert speakers or welding equipment that anyone with a pacemaker should be more concerned about getting in close proximity to," she said.
Ms Moe added that magnets of the strength found in the iPhone 12 could only cause the pacemaker to switch into "a kind of safety mode where the pacing is constant", but it would revert back once the device was removed.
Jo Whitmore, senior cardiac nurse at the British Heart Foundation, echoed the sentiment that patients should not worry if they kept devices at a safe distance, She said: "It's perfectly OK to use a smartphone when you have a pacemaker, and they're designed to return to normal settings once the magnet is moved away."
She added concerned patients should check the device instructions or talk to the manufacturer. They could also contact their doctor or pacing clinic.