Right ventricular volume in 14 fixed hearts from dogs was determined by echocardiography with an algorithm that takes into consideration the crescentic shape of the right ventricular (RV) cross-sectional area. To validate this model the volumes obtained by echocardiography were compared with volumes obtained by water displacement of silicone casts of the same 14 hearts. A strong linear correlation was demonstrated between the echocardiographic volumes and the volumes obtained by water displacement of RV casts (r = 0.96). The results also showed that the echocardiographic volume determination underestimated the RV volume obtained from cast with an almost constant ratio averaging 0.755 as a result of the exclusion of the RV outflow tract volume from the echocardiographic model. We conclude that a crescentic model allows accurate echocardiographic determination of RV volume.