Adding Noise To An ECG Signal

Hi. I m trying to add noise to this ecg signal but ı could'nt understand what is the mistake of my code. How can I add noise to this ecg signal?

clear 
signal = load ('ecgsignals.txt');
plot(signal);
xlabel('Samples');
ylabel('Electrical Activity');
title('ECG Signal Values in 100 Hz');
hold on;
noiseSignal = randn(1, signal);
newSignal = noiseSignal + signal ;
plot(newSignal);

Answer 1

[Walter Roberson]

signal = load ('ecgsignals.txt');
plot(signal);
xlabel('Samples');
ylabel('Electrical Activity');
title('ECG Signal Values in 100 Hz');
hold on;
noiseSignal = randn(size(signal));
newSignal = noiseSignal + signal ;
plot(newSignal);

[MD]

how you take ECG signal as a text? if i taking 100m.mat signal and its showing error. can you describe it?