Diastolic murmurs:

The murmur of tricuspid or mitral valve stenosis is usually heard best at the left middle to left lower sternal borders and may be characterized as a low pitched diastolic rumble.  An example of this is the low pitched mid diastolic rumble of relative tricuspid stenosis as an increased amount of blood including the systemic return and the left to right interatrial shunted blood moves across a normal dimensioned tricuspid valve.  The low pitched mid diastolic murmur of mitral stenosis is common following rheumatic heart disease.  Semi-lunar valvar insufficiency produces an early diastolic murmur with radiation to the apex.  Pulmonary insufficiency is usually of low to medium pitch but may have an early diastolic blowing higher pitch murmur in the presence of elevation of pulmonary vascular resistance such as in Eisenmenger's syndrome (Graham Steell murmur.)  The murmur of aortic insufficiency is characteristically high pitched, blowing early diastolic and heard best at the right second interspace with radiation to the apex.  Aortic insufficiency murmurs may be more easily appreciated in the sitting position with the patient leaning forward in deep exhalation. 

Continuous murmurs:

Patent ductus arteriosus in an older child characteristically is associated with a continuous machinery type murmur heard best at the left middle and left upper sternal border with radiation to the back.  Again, the pitch of the murmur is determined by the pressure gradient between the aorta and the pulmonary artery across the PDA.  A large patent ductus arteriosus may be associated with enough flow from the aorta into the pulmonary artery to elevate the pulmonary artery pressure and would therefore have a medium to low pitch.  A small PDA out side of the newborn period would usually be associated with a high pitched continuos murmur.  Rarely, pulmonary or coronary artery fistulas or arterial - venous malformations may generate a continuous heart murmur.