A 25 year old has a noticeable heart murmur, with a whooshing sound after the lubb (1 st heart sound) heard on auscultation (listening with a stethoscope). This person reports occasional dizziness, particularly on standing. What is the most likely cause of this condition? 1. weak left ventricle 2. open ductus arteriosus 3. running too much 4. leaky bicuspid valve .