Zoll Medical, the maker of devices and software focused on cardiopulmonary and respiratory conditions, has been slammed in an FDA warning letter that outlined numerous quality control and medical device reporting violations.
The regulatory rebuke follows a Form 483 the Chelmsford, Massachusetts-based company was issued last year in the wake of an inspection held between February and April 2025.
The Chelmsford factory produces defibrillators, ventilators, sensors and electrodes and sensors the FDA considered adulterated because “the methods used in, or the facilities or controls used for, their manufacture, packing, storage, or installation are not in conformity with the current good manufacturing practice requirements of the Quality System regulation ,” according to the warning letter dated April 30, 2026.
The agency said Zoll failed to adequately set up and maintain a proper corrective action plan (CAPA) in the wake of being issued a Form 483, and dropped the ball on procedures for validating device design. Specifically, it “failed to verify and validate the labeling change of your 731 MRI compatible ventilators adequately.”
Zoll was also cited for failing to validate device design, which also requires a risk analysis.
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With respect to the compatibility issues of the 731 ventilators, the agency said the risk was calculated only by using 24 malfunctions and 27 complaints related to the device defect.
Even though the company’s own evaluation categorized the risk as life-threatening, it determined the likelihood of a potential hazardous event as “remote”, FDA inspectors found there were 50 complaints, not 27, between 2016 and 2024.
The inspection also found the risk analysis for Zoll’s X Series defibrillators was ineffective and it failed to assess the risk of visible corrosion spots of its One Step electrode used for defibrillation and ECG monitoring.
The FDA also took Zoll to task over its devices being misbranded under federal lay.
For example, the agency said, the company failed to report an incident that indicated one of its ventilator’s malfunction while operating near an MRI. Such an event is required to be reported within 30 days and as it is considered to be a life-threatening occurrence.
“Your firm became aware of the event on June 20, 2024, and FDA received the MDR for the corresponding incident on March 10, 2025, which is beyond the 30‐calendar day timeframe,” the regulator said.
In 2024, Zoll—along with Philips and Baxter—were part of a Class I recall by the FDA that targeted problems with their respective ventilators. Zoll, for its part in that recall, said it would update the operator’s guide and quick reference materials to make it clear how far the ventilator should be placed from an MRI machine, based on the strength of the magnetic field.
