Theoretical and experimental investigations of the relaxation rates of multiple-quantum coherences during heteronuclear double resonance (HDR) pulse sequences are presented. Average Liouvillian theory yields analytical expressions to describe the effective relaxation rates of multiple-quantum coherences during HDR irradiation. Experiments were carried out on a C-13-H-1 pair in glycerol to measure the effective auto- and cross-relaxation rates of multiple-quantum coherences during HDR schemes. The experimental results exhibit a very good agreement with theoretical predictions, even when the average Liouvillian expansion is truncated to zeroth order.