HMR 1098 is not an SUR isotype specific inhibitor of heterologous or sarcolemmal KATP channels

►HMR1098 has been considered a cardiac-specific KATP channel blocker. ►We investigated chamber specificity of HMR action. ►Atrial (SUR1) channels are actually more sensitive than ventricular (SUR2A) channels. ►HMR is more effective on recombinant SUR1-based than SUR2A-based KATP channels. ►The data have implications for use of HMR1098 to probe cardiac KATP.