Heart rate at this moment will be pretty moderate or low, Vigorous and dangerous is kind of vague cause of the fact that, Laughing hard or extremely hard only boost the heart rate to some mediocre levels.
One study suggests which was conducted by a team of professional doctors, Laughing increases the heart to beat and instead conserves the potential risk of cardiovascular related diseases. Laugh as much as you can to avoid potential dangerous.
So, In this context, Laughing will only increase the heart rate to a Moderate level or maintain a low level. It doesn't matter what the context suggests more or less, if "Tracks" is suggested then I'd better say that they are going to have a increased heart beat rate approximately "Vigorous" or "Moderate" But I don't know if it is anything else rather the strings made it clear after all.
Hope helps ...
