Background The precise mechanism of takotsubo-like left ventricular (LV) dysfunction remains unclear. Methods and Results Eight consecutive patients with takotsubo-like LV dysfunction were studied. In the acute phase and 3 weeks later, the coronary flow velocity spectrum and coronary flow velocity reserve (CFVR) were recorded by Doppler guidewire. The deceleration time of diastolic velocity (DDT; ms) was measured from the peak diastolic velocity to the point where the extrapolated line intersected the baseline. In all cases, CFVR of the 3 coronary arteries increased during follow-up (1.7±0.5 to 2.4±0.5 for the left anterior descending artery (p<0.05), 1.7±0.5 to 2.7±0.8 for the left circumflex artery (p<0.05) and 1.7±0.3 to 2.5±0.4 for the right coronary artery (p<0.05)). In addition, the DDT of all coronary arteries increased during follow-up. Conclusions Decreased CFVR and short DDT were demonstrated in patients with takotsubo-like transient LV dysfunction in the acute phase, and these findings improved 3 weeks later, which suggests that coronary microvascular dysfunction may be a causative mechanism. (Circ J 2005; 69: 934 - 939)