Cardiac Arrest

You channel profane magic directly into a target's heart to force it to stop beating. Choose one living humanoid creature of Medium size or lower within 30 feet. That target must make a series of three consecutive Constitution saving throws. For each failed Constitution saving throw, the target takes necrotic damage equal to 33% of their maximum hit points (rounded down). This spell cannot kill its target upon reduction to zero hit points, but renders its target unconscious as the victim’s heart attempts to stabilize itself. If the target of this spell is reduced to zero hit points, the target must make their death saving throws at Disadvantage. 

For every failed Constitution saving throw, the caster’s maximum hit points are reduced by 1d12. This reduction to the caster’s maximum hit points is removed upon a successful Long Rest. Once a target has been affected by this spell, the target becomes immune to this spell for the next week.