What does 'C' Wave in JVP indicate?

A, C and V waves of JVP occur secondary to pressure changes in the atria which are transmitted to the great veins. The c wave is the transmitted manifestation of the rise in atrial pressure produced by the bulging of the tricuspid valve into the atria during isovolumetric ventricular contraction. Ref: Ganong's Review of Medical Physiology, 23rd Edition, Chapter 31