Chordae tendinae in the heart are found in

Purkinje's fibres of the vertebrate heart are modified:

Match the valves of the human heart in column $I$ with the respective opening they guard in column $II$ and select the correct option.

Column $I$	Column $II$
$i$. Eustachian valve	$a$. Opening of pulmonary aorta
$ii$. Thebesian valve	$b$. Left atrioventricular aperture
$iii$. Mitral valve	$c$. Opening of inferior vena cava
$iv$. Semilunar valve	$d$. Opening of coronary sinus

In humans,the sinus venosus is considered to have merged with the wall of which chamber?

Why do cardiac muscles never get fatigued?

If the tricuspid valve of a human heart is partially non-functional due to an injury to the chordae tendineae,which of the following will be immediately affected?