In this work we have studied the effects of heavy ion beam irradiation on a field programmable gate array (FPGA). We have essentially investigated the single event effects (SEE) induced by ions having linear energy transfer (LET) values between LET=1.6 MeV·cm2/mg and LET=78 MeV·cm2/mg. Our tests were performed on a device of the APEX family manufactured by Altera Corporation, featuring a SRAM-based configuration memory. The test methodology was based on the implementation of four shift registers (SRs), two of them using the triple-modular-redundant (TMR) technique. The functionality of this circuit was continuously checked during irradiation and every detected error was logged and time-stamped by a control system. Very few single event upsets have been detected in the SRs. On the contrary, we have recorded a large number of single event functional interrupts (SEFIs). SEFIs were induced by SEUs in the SRAM configuration memory. We observed a constant increase of the supply current during irradiation but this effect was not due to single event latch-ups, but to progressive SEU-induced driver contentions or cumulative micro latch-ups. The configuration memory cross section has been calculated from SEFI cross section.