Myocardial ischemia occurs during cardiac surgery and coronary artery angioplasty. If ischemia is short-term or the heart is protected, cellular necrosis can be avoided. Nevertheless, myocardial stunning occurs and can reduce cardiac performance in the hours after ischemia. Such stunning is preceded by a short period of normal or above normal contraction immediately after reperfusion. The time course of this phenomenon was investigated in six anesthetized dogs subjected to a 10-minute total coronary occlusion. Regional contraction was measured in the ischemic zone and in a remote zone of the heart with a sonomicrometer. Remote zone contraction increased during ischemia, returned toward baseline values after reperfusion, and was stable for the next hour, indicating little effect of time on the experimental preparation. In contrast, ischemic zone contraction was abolished by 10 minutes of coronary occlusion, returned to baseline or greater levels within 1 to 3 minutes following release of the occlusion, then gradually declined over 10 to 20 minutes to a level about 40% below baseline values, indicating myocardial stunning. These findings support the notion that a honeymoon period of normal or above normal function exists during early reperfusion, and that stunning manifests later. This reperfusion "honeymoon" may create a false sense of security.