Heteronuclear long-range correlation experiments are crucial experiments to connect structural fragments via nonprotonated carbons or across heteroatoms, and, currently, there are a plethora of proton-detected methods available for long-range heteronuclear shift correlation [1].
The oldest and still, quite likely, most widely used long-range heteronuclear shift correlation experiment is the HMBC experiment described in 1986 by Bax and Summers [2]. Among the important issues associated with the HMBC experiment [3-4], it is commonly admitted that the Σcos(πⁿJ_HHΔ) term, originating from the homonuclear proton proton couplings can cause accidental cancellation of cross-peaks. However, as will be shown in this contribution, this assumption appears incorrect, and cross peaks in HMBC only vanish when the long-range coupling evolution delay, Δ, matches the long-range heteronuclear coupling constant, Δ = 0.5/ⁿJ_CH. As such, it appears that HMBC-based experiments are more robust than HSQC-based experiments optimized for long-range couplings (LR-HSQC or HSQMBC), because the possibility that long-range cross peaks are missing due to a particular combination long-range coupling evolution delay-long-range heteronuclear coupling constant-homonuclear coupling constant is much lower in HMBC-based experiments. 

[1] G. E. Martin, C. E. Hadden, J. Nat. Prod. 2000, 63, 543-585.
[2] A. Bax, M. F. Summers, J. Am. Chem. Soc. 1986, 108, 2093-2094.
[3] J. Furrer, Concepts Magn. Reson., Part A 2012, 40A, 101-127.
[4] J. Furrer, Concepts Magn. Reson., Part A 2012, 40A, 146-169.