BACKGROUND: This study aims to present a novel method for using cardiovascular magnetic resonance (CMR) to non-invasively quantify the variation in pulmonary blood volume throughout the cardiac cycle in humans. METHODS: 10 healthy volunteers (7 males, 3 female, age range 21-32 years) were studied. The blood flow in the pulmonary artery and all pulmonary veins was quantified during free breathing using phase contrast velocity encoded CMR. The difference in flow between the pulmonary artery and the pulmonary veins was integrated to calculate the change in pulmonary blood volume throughout the cardiac cycle. RESULTS: The stroke volumes in the pulmonary artery and the sum of the pulmonary veins were (mean +/- SEM) 103 +/- 6 ml and 95 +/- 6 ml, respectively. The pulmonary blood volume variation (PBVV) was 48 +/- 5 ml, and the PBVV expressed as percent of the pulmonary artery stroke volume was 46 +/- 3%. The maximum increase in pulmonary blood volume occurred 310 +/- 12 ms after the R-wave from the ECG (32 +/- 2% of the cardiac cycle). PBVV did not correlate to change in cross-sectional area in the pulmonary artery (R2 = 0.03, p = 0.66). CONCLUSION: It is feasible to non-invasively quantify the change in pulmonary blood volume during the cardiac cycle in humans using CMR. The average pulmonary blood volume variation in healthy volunteers was approximately 50 ml and this was approximately 50% of the stroke volume. Further studies are needed to assess the utility of the pulmonary blood volume variation as a measure for identifying cardiac and pulmonary vascular disease.