A 41-year-old man was referred to our hospital suffering from pyrexia. Echocardiogram showed diffuse severe hypokinesis of the left ventricle. The patient was treated medically under a diagnosis of acute myocarditis and anticoagulation therapy had been started. However a large mobile thrombus and multiple small thrombi were detected in the left ventricle 2 days after admission. Because of the deterioration of his left ventricular function (LVEF 14%), he was treated medically with careful monitoring of the thrombi by echocardiogram. His left ventricular function started to improve 3 days after admission (LVEF 27%), and then surgical removal of the thrombi was performed through left ventriculotomy. His postoperative course was uneventful. LVEF was improved to 60% at discharge. He is doing well without any signs of embolic event at 2 years postoperatively. Left ventriculotomy is one of the useful methods for removal of left ventricular thrombus associated with acute myocarditis, if the procedure is performed during the recovery phase.