I sneezed yesterday and started feeling breathless and still do today is this a result of allergies my asthma or my heart murmur?

Allergies and asthma: Although some heart conditions that cause heart murmers can be associated with shortness of breath, the combination of sneezing and breathlessness is most likely to be due to a flar in your allergies and asthma, or due to a new upper respiratory infection. If using your allergy and asthma medications as instructed does not provide you with relief, or if new symptoms develop, schedule a visit.