Key points are not available for this paper at this time.
A reliable method of determining the presence of a pericardial effusion has been evolved. Ultrasonic waves reflected from the posterior part of the anterior chest wall and from the anterior surface of the anterior myocardium and pericardium produce echoes separated from each other by a bare area. This bare area varies in width and the variation has the same periodicity as the cardiac cycle.
Pridie et al. (1968) studied this question.