Chloroquine and hydroxychloroquine are used to chronically treat certain rheumatologic diseases and are generally considered safe. We describe 2 patients with skeletal myopathy and fatal cardiomyopathy-uncommon and underrecognized adverse effects of these agents. Both patients developed arrhythmias and heart failure, and 1 patient had documented diaphragmatic involvement. Muscle specimens showed typical vacuolar myopathy (indicative of impaired autophagy) with myeloid bodies in both patients and curvilinear bodies in 1 patient. Antimalarial-induced cardiomyopathy should be considered in patients receiving these medications with otherwise unexplained muscle weakness or cardiac symptoms. Whether autophagy enhancers can be used to manage such myopathies merits investigation.