Massive Left Atrial Thrombi during Dabigatran Therapy for Nonvalvular Atrial Fibrillation.

• Massive LA thrombus is rare in the absence of anticoagulation and mitral stenosis. • Direct-acting oral anticoagulants are widely used in nonvalvular AF. • Inadequate dosing of direct-acting anticoagulants may be difficult to recognize. • Consequences of inadequate dosing may be severe.