The administration of a diuretic can reduce the volume and diminish preload so the heart doesn't have to work so hard. Sympathetic stimulation can enhance preload by causing blood vessels to constrict and return more blood to the left ventricle. This stimulation also augments the force of the contraction and the heart rate, ultimately improving cardiac output. However, with an injured myocardium, a faster rate can overwork the heart and have negative consequences. This increases the oxygen demand on the heart and can lead to further myocardial ischemia.
Atrial kick is the volume of blood ejected into the ventricles by contraction of the atria.
Morphine, in addition to relieving pain and anxiety, dilates peripheral vessels. Some patients may experience hypotension due to arterial as well as venous dilation from only small doses, while others may require repeated high doses to achieve a therapeutic effect. Furosemide is an effective diuretic that diminishes total body blood volume by boosting urine output, as long as the heart works well enough to perfuse functioning kidneys. Customary IV doses range from 20mg to 40mg, although the amount may be as great as 100mg in emergency situations. Blood pressure needs careful monitoring when administering IV diuretics, particularly when given to already hypotensive patients, who may need additional medications to support blood pressure during diuresis.