How can I output my generated heart beat signal at high BPM accurately using matlab?

%Code to 1 heart beat signal %---------------------------------------

    Fs = 48000;
    HR = 60 ;  % Heart beat bpm (range 60 - 200Bpm);
    pulse_width = 60e-3;
    Amp = 0.5;

    delay = ((60/HR)/2)-(0.5*pulse_width);

    t1 = -delay:(1/Fs):delay;

    Heartbeat = Amp*tripuls (t1,pulse_width);

   % plot ( t1, Heartbeat);

    % Output signal to heart rate monitor
    while (1)
    sound(Heartbeat,Fs);
    end

I'm having problem outputting my generated Heart beat signals, when I play the signal using Sound in matlab and measure it on an external heart rate monitor. I get a different reading to the simulated value. But seem to be correct only at 60 Bpm to maybe 100 Bpm. Need to include heart rates up to 200 Bpm. In order words, I get a lot of unstable output at high Bpm.