Two hospital staff members have been suspended over potential instances of inappropriate access connected to the Southport attack.
Liverpool Heart and Chest Hospital is carrying out an investigation after the cases were detected as part of a retrospective audit.
The two staff members have been placed on precautionary suspension while the investigation is concluded.
The hospital said leaders have contacted those affected.
The matter has also been reported to the Information Commissioner's Office and the Care Quality Commission.
Manoj Kuduvalli, medical director for Liverpool Heart and Chest Hospital, said: "We are deeply sorry that this has happened.
"Our patients trust us with their most personal information at some of the most vulnerable moments in their lives, and any inappropriate access to those records is a serious violation of that trust.
"We have been clear with all colleagues that patient records must only ever be accessed for legitimate reasons connected to their role and the patient's care.
"We will not accept behaviour that compromises patient confidentiality or undermines the trust our patients place in us.
"We have spoken to those that are affected and will keep them informed as our investigation continues."
Earlier this year, a Southport stabbing survivor said she was "absolutely devastated" after it emerged that 48 hospital workers had inappropriately accessed the medical records of victims.
Some of those injured were treated at University Hospitals of Liverpool Group, to which the Heart and Chest Hospital belongs.
A Sky News investigation last month found Nottingham and Southport data NHS breaches were "the tip of the iceberg".
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