A case of transient left posterior hemiblock and various intraventricular conduction disturbances associated with acute anterolateral infarction is reported. The earliest manifestation was an appearance of ventricular premature systoles originated in the area of the left posterior fascicle. On following recordings left posterior hemiblock with periods of high grade A-V block developed. A few minutes later regular alternation of left posterior hemiblock and left anterior hemiblock was recorded in the presence of 2:1 A-V block. The mechanism for such rare manifestation is analysed. After representing complete left bundle branch block, spontaneous recovery of normal conduction was obtained without any change in heart rate.