Sarco(endo)plasmic reticulum calcium (Ca2+) ATPase 2a (SERCA2a) regulates cardiac function by removing cytosolic Ca2+. SERCA2a is altered by the post-translational modification, acetylation. However, the effect of acetylation on SERCA2a in the diseased human heart is not understood. Therefore, this case-control study examined SERCA2a acetylation in the right atrium (RA) of the diseased human heart. To accomplish this, human RA tissue samples were obtained from 61 patients undergoing cardiac surgery. Tissue collected was categorized based on heart disease type (i.e. heart valve disease (HVD) or coronary artery disease (CAD)), the absence or presence of systolic dysfunction (SD), and type 2 diabetes (T2D) status. The objectives of this study were to determine (1) if RA SERCA2a acetylation and SERCA function are altered by heart disease type; (2) if RA SERCA2a acetylation and function are altered by the presence of SD; (3) if RA SERCA2a acetylation and function are altered by T2D status. RA SERCA2a acetylation was altered by heart disease type, as there was a 53% difference in RA SERCA2a acetylation between patients with HVD or CAD (p = 0.012). A 31% difference in RA SERCA Vmax was identified between patients with HVD or CAD (p = 0.004). RA SERCA2a acetylation was not altered by SD or T2D independently, but RA SERCA2a acetylation was increased by 3-fold in patients with combined SD and T2D, compared to patients with T2D alone (p = 0.013). SERCA Vmax was 22% higher in the RA of patients with SD, compared to patients without SD (p = 0.020). The SERCA Hill coefficient was 29% greater in the RA of patients with T2D, compared to patients without T2D (P = 0.021). A positive relationship was found between RA SERCA2a acetylation and RA SERCA Vmax using unadjusted linear regression analysis (r = 0.36; r2 = 0.13; p = 0.034). Our study is the first to reveal differences in RA SERCA2a acetylation and SERCA function based on heart disease type, the presence of SD, and T2D status.