Cardiac Arrest (Overkill Supplement)
From D&D Wiki
Sometimes it may be interesting for a player or non-player character to suffer a potentially fatal heart attack. A creature which undergoes cardiac arrest immediately falls unconscious, and must succeed on a DC 20 Constitution saving throw or suffer a level of exhaustion. The creature must repeat this saving throw every minute thereafter until it succeeds three times or it dies. If a creature with proficiency in the Medicine skill remains within 5 feet of the creature and gives the creature full, uninterrupted medical attention, that creature may add its proficiency bonus to the saving throw of the creature undergoing cardiac arrest. If a creature survives cardiac arrest, it remains unconscious for 1d4 hours. A Greater Restoration spell can end this condition on a creature in lieu of its other effects, while a Heal spell can end this condition in addition to its other effects. Lesser spells are not powerful enough to make a meaningful difference. Heart attacks are extremely dangerous and can kill in a matter of minutes.