MATLAB: How to do FFT from signal figure

i used this code to plot ecg signals, now how can i use FFT (fast fourie transform ) code to my signal ?

function plotATM(a02m)

infoName = strcat('a02m', '.info');

matName = strcat('a02m', '.mat');

Octave = exist('OCTAVE_VERSION');

load(matName);

fid = fopen(infoName, 'rt');

fgetl(fid);

[freqint] = sscanf(fgetl(fid), 'Sampling frequency: %f Hz Sampling interval: %f sec');

interval = freqint(2);

fgetl(fid);

if(Octave)

for i = 1:size(val, 1)

R = strsplit(fgetl(fid), char(9));

signal{i} = R{2};

gain(i) = str2num(R{3});

base(i) = str2num(R{4});

units{i} = R{5};

end

else

for i = 1:size(val, 1)

[row(i), signal(i), gain(i), base(i), units(i)]=strread(fgetl(fid),'%d%s%f%f%s','delimiter','\t');

end

fclose(fid);

val(val==-32768) = NaN;

for i = 1:size(val, 1)

val(i, 🙂 = (val(i, 🙂 – base(i)) / gain(i);

end

x = (1:size(val, 2)) * interval;

plot(x', val');

for i = 1:length(signal)

labels{i} = strcat(signal{i}, ' (', units{i}, ')');

end

legend(labels);

xlabel('Time (sec)');

% grid on

end

thanks