ಇಲ್ಲ ಮಹೇಶ್,
Technically speaking, 'contraction' and 'relaxation' - are the correct and specific terms.
Basically heart is made up of cardiac muscles and muscles do not expand. They can oly contract or relax.
Energy is required for contraction- because it is an active process. Relaxation is mostly a passive process.
May be relaxation can not be translated as ವಿಶ್ರಾಂತಸ್ಥಿತಿ. But we need to esarch some other term.
ಕನ್ನಡದಲ್ಲಿ ಬರೆದರೆ ಗೊಂದಲ ಇನ್ನೂ ಹೆಚ್ಚಾಗಬಹುದೆಂಬ ಕಾರಣಕ್ಕಾಗಿ ಇಂಗ್ಲಿಷ್ ನಲ್ಲಿ ಬರೆದಿದ್ದೇನೆ. ಕ್ಷಮಿಸೋಣವಾಗಲಿ.