During the August 1983 outburst of the old nova GK Persei observations with EXOSAT showed for the first time a 351 second periodicity in X-rays. Our fast photometry (U(B)V with 25 sec time resolution) was made at the end of the outburst in the nights of September 29, and October 1 3, using the 2.2 meter telescope at Calar Alto (Spain). Optical variations up to 10% in U and 4% in V with periodicities in the range 350 to 360 seconds were found, lasting only for few cycles. A comparison with the extrapolated prediction of the X-ray maxima did not show a coincidence, but rather an anticoincidence in several cases. This supports a model of reprocessed X-rays at the inner edge of an accretion disk.