If you are administering a furosemide (Lasix) which is a loop diuretic and NOT cardiovascular drug (although it is used in Congestive Heart Failure to relieve edema and decrease preload). You need to take into consideration the electrolytes that the patient will loose by voiding, a very important electrolyte is potassium. If the patient looses a lot of potassium (hypokalemia) and if you give a cardiovascular drug like Digoxin (Lanoxin), it can potentiae digitalis-induced arrhythmias.