The presence of the combination of relief of chest pain, normalization of ST-segment changes, and reperfusion arrhythmias has been found to be indicative of coronary recanalization, but these criteria are not sensitive, because all 3 occur in only 15% of patients.13 A retrospective assessment of the efficacy of reperfusion can be performed, based on CK and CK-MB washout curves, which can also provide a rough estimate of the extent of cell injury. More specific parameters of cell death are provided by the measurement of the myofibrillar troponin proteins, which exist in a large structurally bound pool, but in low cytosolic concentrations.1 This compartmentalization is responsible for the biphasic release pattern, most pronounced for troponin T, that is seen after successful reperfusion (Figure 1, top).24 The cytosolic pool is rapidly washed out and is responsible for the first distinct peak, occurring after approximately 14 to 16 hours. A long plateau follows (until day 5 after acute myocardial infarction) or a second peak value occurs during day 4 (around 96 hours) (Figure 1, inset), representing disintegrating myofibrils.24 In patients who have not undergone reperfusion, troponin T levels increase unsteadily (Figure 1, bottom). Furthermore, biochemical assessment of reperfusion therapy would be most valuable at times when mechanical intervention, such as rescue angioplasty, could still be of benefit to the patient.1 In an angiographically controlled study, Abe et al27 demonstrated that serial measurements of troponin T are excellent indexes of reperfusion at 1 hour (Figure 2). The kinetics of troponin T release differ markedly in relation to reperfusion and can therefore be used to indirectly assess coronary artery patency. Similarly, cardiac troponin I has been shown to be advantageous for the early, noninvasive determination of coronary reperfusion following thrombolytic therapy. With documented angiography at 90 minutes, Apple et al28 demonstrated a significantly larger percentage of change from baseline value in cardiac troponin I concentration with reperfusion as compared with concentrations of CK-MB and myoglobins (Figure 3). They found the sensitivity for detecting reperfusion at 90 minutes for the cardiac troponin T, myoglobin, and CK-MB levels to be 82.4%, 76.5%, and 64.7%, respectively.