A 34-yeаr-оld mаle with а histоry оf nonischemic cardiomyopathy (NICM) thought to be related to a familial etiology presents to the ED with complaint of worsening shortness of breath and lower extremity edema. He is on home Milrinone at 0.375 mcg as he waits on the heart transplant list status 1A. His vital signs show a temperature of 100.5, HR 127, RR 28, BP 115/67, and O2 sat of 96% on RA. An echocardiogram is ordered and shows an ejection fraction of 20-25%. All of the following can increase myocardial contractility EXCEPT.