The heteronuclear single quantum coherence or heteronuclear single quantum correlation experiment, normally abbreviated as HSQC, is used frequently in NMR spectroscopy of organic molecules and is of particular significance in the field of protein NMR. The experiment was first described by Geoffrey Bodenhausen and D. J. Ruben in 1980.  The resulting spectrum is two-dimensional (2D) with one axis for proton (H) and the other for a heteronucleus (an atomic nucleus other than a proton), which is usually C or N. The spectrum contains a peak for each unique proton attached to the heteronucleus being considered.  The 2D HSQC can also be combined with other experiments in higher-dimensional NMR experiments, such as NOESY-HSQC or TOCSY-HSQC.