50 years old is brought to emergency department for evaluation of fever, chills, malaise and fatigue. Cardiac examination reveals a new holosystolic murmur that radiates towards the axilla. Blood cultures are obtained. He undergoes a transoesophageal echocardiography. The USG probe is placed in mid oesophagus facing anteriorly and the cardiac chambers are interrogated. The chamber which is anatomically closer to the probe is