Question

On ECG, during which interval are all parts of the myocardium relaxed?

Answer 1

1 cardiac cyle lasts for 0.8 second.

and out of 0.8 sec the entire myocardium is relaxed for 0.4 sec

QRS complex represents ventricular systole. the atrial repolarisation/ atrial diastole merges with it.

the ST segment is a long isoelectric point and measures the time from ventricular systole to ventricular diastole.

now remember that atria was already in diastole from the time ventricles started contracting and QRS complex had appeared.

and this is the time (after ST segment) when both the ventricles and atrial muscles are relaxed. and is represented as T wave on the ECG

look into the diagram for better understanding