Looping a movie clip symbol from a different point in the timeline (HTML5)

I am trying to loop a movie clip symbol. I want the loop to start at a later point in the timeline so that the double-pulse plays once, then only one pulse plays for the rest of the duration. However, when I tried to code this in HTML5, the single pulse plays as a wave. The code is called in the internal timeline of the pulses on the last frame of the loop, which is a blank keyframe. 

Here is the code I am using for the pulses:

var _this = this;

this.play();

if (frameLabel == 'SinglePulse') 

	this.gotoAndPlay('SinglePulse')