A 49-year-old patient complains about pain in the oral cavity induced by eating. He suffers from CHD. Objective examination revealed dyspnea, limb edema. Oral cavity isn't sanitated. On the mucous membrane on the right, there is an ulcer with irregular edges covered with greyish-white necrotic deposit with low-grade inflammation around it. There is also halitosis. What is the most probable diagnosis?