S4

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S4

Symbol for fourth heart sound.

S4

the fourth heart sound in the cardiac cycle. It occurs late in diastole on contraction of the atria. Rarely heard in normal subjects, it indicates an abnormally increased resistance to ventricular filling, as in hypertensive cardiovascular disease, coronary artery disease, cardiomyopathy, and aortic stenosis. A left-sided fourth heart sound, it may be heard with the stethoscope's bell at the apex of the heart during expiration. Also called atrial gallop, physiological fourth heart sound.

S4

1. Fourth heart sound, which corresponds to atrial contraction during presystole; it is rarely heard in normal hearts.

S4

Abbreviation for fourth heart sound.
References in periodicals archive ?
In February, Luna filed a Form S-4 registration statement with the Securities and Exchange Commission with respect to the proposed merger.
The command team is led by cither an Air Force lieutenant colonel or a Navy commander; the PRT commander's branch of service will coincide with the branch of the enlisted personnel in the S-l, S-4, S-6, and information operations staff sections.
The company added that the SEC form S-4 registers Endo's ordinary shares to be issued in connection with the pending acquisition of Auxilium Pharmaceuticals.
This Form S-4 contains proxy material related to the required approval of the deal by Mesa Energy shareholders.