Permanent ventricular paroxysmal tachycardia was observed in a 3-year-oldΔ Thoroughbred colt. The diagnosis of this disease was made on the basis of the following electrocardiographic findings : (a) Runs of the QRS comlexes in succession at the rate of 152 per minute, the configuration of which was like that of ventricular premature beat. (b) Slower regular atrial rhythm at the rate of 69 per minute showing AV dissociation. (c) Occasional appearance of ventricular capture. Clinical, electrocardiographic, phonocardiographic and sphygmomanometric studies revealed the significance of the arrhythmia on circulatory dynamics. Detachycardia was unsuccessfully tried with quinidine sulfate. The present case was considered as a primary heart condition due to the ectopic pacemaker in the ventricular septal lesion,
