Feeling short of puff can obviously be due to a number of things. It also depends if the shortness of breath comes on suddenly or has been gradually getting worse over weeks/months/years. It occurs because the body is not getting the amount of oxygen it needs to do what is being asked of it.
This can be because there isn’t enough oxygen available to the person (being suffocated or something stopping the oxygen getting down to the lungs). The lungs may not be working properly (asthma, emphysema, chest infections, fluid in the lungs or some form of trauma). It’s also possible the oxygen can’t get from the lungs into the blood system (problem with the blood itself, blood clot in the lung or heart not pumping properly).
We could write a whole book just about shortness of breath, so obviously, the explanation & advice given here will be very limited. We’re going to concentrate on the heart causes of shortness of breath (since this website has been written by a cardiologist!).