Final answer:
The 'lubb' or first heart sound is related to the ventricular systole phase on an ECG and corresponds to the R wave, representing ventricular depolarization and the start of their contraction.
Step-by-step explanation:
The first heart sound, "lubb," is heard when the atrioventricular (AV) valves close, and this is related to the ventricular systole on an electrocardiogram (ECG). During ventricular systole, the ventricles contract and increase the pressure inside them, preventing the backflow of blood into the atria and leading to the closure of the tricuspid and mitral valves, thus producing the "lub" sound. This event typically corresponds to the R wave on an ECG, which represents the depolarization of the ventricles prior to their contraction.