Functional murmurs are short, early systolic or midsystolic murmurs of grade 2/6 or less that are well-localized to the area of the left sternal border and diminish in intensity when the patient stands, sits up, or strains during the Valsalva maneuver.

Not loud, short duration, disappear with cahnge in body position,no pathological abnormality of heart
eg prominent in fever anxiety anemia infections
 pulmonary and aortic ejection systolic murmur in hyperdynamic states
ejection sys murmur in asd

organic murmur indicates pathological abnormality causing heart murmur
it is loud,long duration,noise constant doesnot change with body position,diastolic filling murmurs,mitral or tricuspid stenosis ,atrial myxoma
eg narrow valve,leaking valve

Functional murmurs are always systolic and never associated with a thrill. They can be heard in physiological states such as pregnancy.