There are four important areas used for listening to heart sounds. These are: Aortic area, Pulmonic area, Tricuspid area, Mitral Area (Apex).
A common notation for a sound heard at an auscultatory site is to use the first initial of the site and the number 1 or 2 to describe the first or second heart sound respectively. Thus T1 denotes the first heart sound at the tricuspid area; M2 denotes the second sound at the mitral area, etc. In general both the first and second sounds can be heard at all sites, but some pathologic and normal sounds are heard best at one site or another. Gallops are often best heard at the apex as is M1 and T1. T1 is slightly louder at the tricuspid position. The A2 and P2 are best heard at the aortic and pulmonic sites respectively with the A2 sound being the major component of the second sound heard at the apex.
The first heart sound consists of four components. The most notable components are two large, high amplitude deflections, M1 - related to mitral valve closure - and T1 - related to tricuspid valve closure. The second heart sound consists of high frequency deflections relating to the closure of aortic and pulmonic valves. Transit time through the lungs causes a delay between generation of these two sounds causing the aortic sound to be noted some 40-85 milliseconds before the pulmonic sound (A2 and P2 respectively). Variability of the pulmonary vascular impedance with respirations causes prolongation of the time period between A2 and P2 with inspiration and a decrease in the interval with expiration.
Sounds related to mitral and tricuspid valves (atrioventricular
valves) opening and closing can de defined relatively easily at the
apex. At this point, opening
snaps and nonejection sounds can also be heard. Sounds related
to the second heart sound include the opening and the closing of aortic
and pulmonic valves (semilunar valves), and early ejection clicks.