The purpose of this study was to determine the effect of different microbubble gases on the amount of myocardial contrast (MC) produced from intravenously (IV) injected dextrose albuinin microbubbles when using a new imaging modality termed transient response imaging (TRI). In 6 dogs (4 closed chest, 2 open chest) the peak anterior myocardial videointensity (PMVI) and visual degree of MC were determined following IV injections of equivalent doses of perfluorocarbon exposed sonicated dextrose albumin (PESDA), sulfur hexafluoride-exposed sonicated dextrose albumin (SHESDA), and room air exposed sonicated dextrose albumin (RASDA) microbubbles. TRI was performed by triggering ultrasound impulses to 1 point every one to two cardiac cycles. The PMVI produced with TRI was compared to conventional 30 Hz frame rate imaging (CI) for each gas. Visual anterior and posterior MC was evident with TRI in all six dogs using PESDA, but not in any dog with CI. Although RASDA and SHESDA did not produce MC with CI, visually evident anterior MC was seen after 7 of 8 SHESDA and 4 of 9 RASDA injections when using TRI with both gases. PESDA produced the highest peak PMVI of all three microbubbles when using TRI, while SHESDA produced a significantly higher PMVI than RASDA. We conclude that although MC can be produced with TRI using microbubble gases of lower molecular weight, the brightest and most consistent contrast is produced with fluorocarbon containing microbubbles.