PDE3 inhibitors are a type of phosphodiesterase inhibitors . Inhibition of the PDE isoenzyme 3 leads to an increase of intracellular concentrations of the second messenger cyclic adenosine monophosphate (cAMP). cAMP mediates the phosphorylation of protein kinases , which in turn activates cardiac calcium channels . An increased calcium influx from the sarcoplasmic reticulum (SR) during phase 2 (the plateau phase) of the cardiac action potential leads to a positive inotropic effect of PDE3 inhibitors: they increase the force of cardiac contraction. Increased reflux of calcium into the SR following the plateau phase is responsible for their positive lusitropic effect: they increase relaxation speed. Additionally, PDE3 inhibitors act as vasodilators .  
Use cautiously in patients with deficiency of spleen and stomach, or during pregnancy. Chih-ko ( zhiqiao ) To move qi; to ease the middle jiao and eliminate distention. Distention and pain in the epigastrium and abdomen and poor appetite due to stagnation of spleen and stomach qi. 3-10 grams Blue citrus ( qingpi ) To regulate liver and break qi; to disperse lumps and relieve stagnant food. Distending pain in the hypochondriac region and breast, hernia caused by stagnation of liver qi; distending pain in the abdomen and epigastrium due to stagnant food with stagnant qi; movable or immovable masses in the abdomen due to stagnation of qi and blood. 3-10 grams
It seems quite clear that the medical community is blind to the lies that go on and simply take these adverse effect reports according to a 2004 WebMD study of patients, 22% lied about smoking, 16% lied about how much or how often they drink alcohol and 12% lied about recreational drug use. With this taken into consideration, it would appear that synephrine is a very safe supplement considering that it is estimated that over 100 million synephrine containing supplements have been sold, which makes these reports absurd considering that 12 million of the people using synephrine could have also been at risk due to illegal drug use which seems to go unreported to the medical community. Additionally, doctors rarely do a full medical background check before they publish these articles, instead treating each incident independent of the patients medical history.