The fourth heart sound (S4) is an auscultatory marker of left ventricular diastolic dysfunction (LVDD). Additionally, S4 correlates with atrial function, which is typically impaired in patients with Type 2 diabetes (T2D) but can improve with sodium-glucose co-transporter-2 inhibitor (SGLT2i) therapy. This case report highlights the dynamic changes in S4 associated with modification of SGLT2i therapy. An 83-year-old male with T2D and LVDD, confirmed via echocardiography, was treated with SGLT2i therapy for 4 years for glycemic control. The therapy was discontinued in December 2023 because of increased nocturnal urination. Two months after discontinuation, the patient developed pronounced S4, accompanied by mild chest discomfort and worsening of evening leg edema. Resumption of SGLT2i therapy led to a marked reduction in S4 along with a remarkable improvement in chest discomfort and edema within 1 month. These findings were confirmed by visual phonocardiography. This case underscores the potential utility of dynamic S4 changes as a noninvasive indicator of SGLT2i therapy adjustment. These findings highlight the novel clinical application of S4 monitoring in mitigating heart failure progression in patients with T2D.