2 months old w/ holosystolic LLSB murmur -- ONLY holosystolic murmurs are mitral regurg, Tricuspid regurg, VSD PDA - continuous machine like murmur

The location is what helped me out. Left lower sternal border is LV. Mitral regurg would be at apex, PDA would be machine like, coarctation would have weak distal extremity impulses, and patent foramen ovale would be upper sternal border. The only time I've ever heard of Tricuspid regurgitation is with IVDA, which I doubt is going on with the 2 month old boy unless the mom has the propensity to shoot him up and in that case he'd probably present with a fever anyways.