what is the cause of s3 heart sound
Third heart sound S3 is thought to be caused by the oscillation of blood back and forth between the walls of the ventricles initiated by the inflow of blood from the atria. The reason the third heart sound does not occur until the middle third of diastole is probably that, during the early part of diastole, the ventricles are not filled sufficiently to create enough tension for reverberation. It may also be a result of tensing of the chordae tendineae during rapid filling and expansion of the ventricle.
First-degree atrioventricular block The most common causes of first-degree heart block are an AV nodal disease, enhanced vagal tone (for example in athletes), myocarditis, acute myocardial infarction (especially acute inferior MI), electrolyte disturbances and medication. The drugs that most commonly cause first-degree heart block are those that increase the refractory time of the AV node, thereby slowing AV conduction. These include calcium channel blockers, beta-blockers, cardiac glycosides, and anything that increases cholinergic activity such as cholinesterase inhibitors. Digitalis is a sodium/potassium ATPase inhibitor and also prolongs AV conduction.