In a lawsuit against short seller Muddy Waters and security firm MedSec, plaintiff St. Jude Medical faces fresh claims that its heart devices are vulnerable to hacks.

St. Jude Medical yesterday filed a lawsuit alleging that investment research firm Muddy Waters and healthcare security research company Med Sec made false claims in a report focused on the security of St. Jude products. The report released Aug. 25 warned of potentially catastrophic cybersecurity vulnerabilities in St. Jude pacemakers, defibrillators and other medical devices....