Synchronize Serial communication between simulink and Arduino

I am trying to build a model that sends two floats over serial to an arduino and waits for two values to be sent back. For now am trying to send back the same values to ensure that the arduino is reading the values correctly. I think right now I am having a problem were simulink is sending the values so fast that its overflowing the buffer and the arduino is reading garbage.

Is is possible to trigger a Simulink serial send command when it reads a value from the Serial port?