An 11-year-old male castrated Scottish fold cat was presented for perineal urethrostomy after a history of dysuria. Pre-operative examinations, including thoracic radiography and echocardiography, revealed that the cat had an insidious dynamic left ventricular outflow tract obstruction (LVOTO). The cat underwent a perineal urethrostomy under general anesthesia. Invasive arterial blood pressure (IABP) was measured for cardiovascular monitoring during anesthesia. Dynamic blood pressure fluctuation and dicrotic notch disturbance with severe hypotension were suspected from an arterial pressure waveform during surgery. However, the hypotension improved after intravenous administration of ephedrine with careful observation of heart rate and IABP. Invasive arterial blood pressure was a useful monitoring method for general anesthesia in a cat with LVOTO.