The "Stone Heart" Theory in Digoxin Toxicity: A Modern Perspective Stone Heart Syndrome refers to a theoretical, lethal state of sustained myocardial contraction (systolic contracture) due to profound intracellular calcium overload. In digoxin toxicity, this was hypothesized to occur when IV calcium administration exacerbates the digoxin-induced inhibition of the Na /K -ATPase pump, which already causes elevated cytosolic calcium. The result is a non-relaxing, "stone-like" heart incapable of fil