The terms Lubb and Dubb relate to which one of the following?

The terms 'Lubb' and 'Dubb' (or 'Lub' and 'Dub') refer to the two primary sounds produced during a cardiac cycle, which are audible through a stethoscope [t2][t3]. The first heart sound (S1), described as 'Lubb', is produced by the simultaneous closure of the atrioventricular valves (mitral and tricuspid) at the onset of ventricular systole [t2][t5]. It is characterized as a long, soft, and low-pitched sound [t5][t7]. The second heart sound (S2), described as 'Dubb', occurs due to the closure of the semilunar valves (aortic and pulmonary) at the beginning of ventricular diastole [t2][t6]. These sounds are essential for clinical diagnosis, as variations can indicate valvular diseases or other cardiac issues [t3][t5]. While the heart also produces third and fourth sounds, they are typically inaudible in normal conditions and require specialized equipment like a phonocardiogram for detection [t3][t8].

Sources

1. [1] https://www.ncbi.nlm.nih.gov/books/NBK333/
2. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC6864449/