how can I merge to wav files with a pause of 3 seconds between them?

merged_fs = max(fs1, fs2);
merged_wav = [reshape(wav1, fs1, merged_fs); zeros(merged_fs * 3, size(wav1, 2); reshape(wav2, fs2, merged_fs)];

This can be made simpler if the two are the same sampling frequency, fs

merged_wav = [wav1; zeros(fs * 3, size(wav1, 2)); wav2];

Note: this code expects that the wav files have the same number of channels.