What Is the Most Common Cause of Upper Gastrointestinal Bleeding

Mr. Santos, a 65-year-old Male, Presents to the Emergency Department with Complaints of Black, Tarry Stools for the Past Two Days. He Reports Feeling Weak and Lightheaded. on Physical Examination, His Blood Pressure Is 90/60 Mmhg, Heart Rate Is 110 Beats Per Minute and He Appears Pale. Laboratory Results Show a Hemoglobin Level of 8 G/dl (Normal Range: 13.5-17.5 G/dl)