For multiple FPGA systems, the limited number of I/O pins causes many problems. To solve these problems, efficient communication scheduling among FPGAs is crucial for obtaining high CLB utilization. In this paper, we show that the communication scheduling problem is NP-complete and provide a heuristic scheduling algorithm. The experimental results show that our algorithm generates excellent communication schedules: more than 90% of the randomly generated problem instances were scheduled with less than 20% overhead compared with an optimal algorithm. The execution time of the scheduling algorithm is two orders of magnitude less than the optimal scheduling algorithm.