A sterile non-pyrogenic suspension of microspheres of human serum albumin with the stable, high-molecular-weight fluorocarbon gas perflutren, used as a contrast enhancement agent for ultrasound procedures. Because the acoustic impedance of perflutren protein-type A microspheres is much lower than that of blood, impinging ultrasound waves are scattered and reflected at the microsphere-blood interface and may be visualized with ultrasound imaging. At the frequencies used in adult echocardiography (2-5 MHZ), the microspheres resonate which further increases the extent of ultrasound scattering and reflection.