Myocardial uptake using (99m)Tc-sestamibi single photon emission computed tomography (SPECT) depends largely on myocardial microvascular volume. Myocardial contrast echocardiography (MCE) is a relatively new technique that detects not only microvascular volume but also blood flow. These differing mechanisms may affect the relative accuracies of MCE and SPECT for detecting myocardial viability (MV) early after acute myocardial infarction (AMI) and thrombolysis. Accordingly 56 patients underwent resting transthoracic echocardiography, low-power MCE and SPECT 7+/-2 days following first AMI and thrombolysis. Contractile reserve (CR) was assessed 3 months following revascularization. The sensitivity and specificity of MCE and SPECT were 83% and 78% (p=ns) and 78% and 45% (p<0.01) respectively. MCE was the only multivariate predictor of global recovery of function and CR (OR=3.5, p=0.01). The different physiological mechanisms employed by MCE and SPECT translate into different relative accuracies for the detection of MV.