L oss of cardiac myocytes in heart failure is thought to occur largely through an apoptotic process. Here we show that heart failure can also be precipitated through myocyte necrosis associated with Ca²⁺ overload. Inducible transgenic mice with enhanced sarcolemmal L-type Ca²⁺ channel (LTCC) activity showed progressive myocyte necrosis that led to pump dysfunction and premature death, effects that were dramatically enhanced by acute stimulation of β-adrenergic receptors. Enhanced Ca²⁺ influx–induced cellular necrosis and cardiomyopathy was prevented with either LTCC blockers or β-adrenergic receptor antagonists, demonstrating a proximal relationship among β-adrenergic receptor function, Ca²⁺ handling, and heart failure progression through necrotic cell loss. Mechanistically, loss of cyclophilin D, a regulator of the mitochondrial permeability transition pore that underpins necrosis, blocked Ca²⁺ influx–induced necrosis of myocytes, heart failure, and isoproterenol-induced premature death. In contrast, overexpression of the antiapoptotic factor Bcl-2 was ineffective in mitigating heart failure and death associated with excess Ca²⁺ influx and acute β-adrenergic receptor stimulation. This paradigm of mitochondrial- and necrosis-dependent heart failure was also observed in other mouse models of disease, which supports the concept that heart failure is a pleiotropic disorder that involves not only apoptosis, but also necrotic loss of myocytes in association with dysregulated Ca²⁺ handling and β-adrenergic receptor signaling.