Which of the following findings indicates that dopamine therapy in a heart failure patient is effective?

Dopamine therapy in heart failure patients is aimed at improving cardiac output by enhancing myocardial contractility and facilitating better blood flow. When dopamine is effective, one of the primary indicators is an increase in cardiac output. This reflects the heart’s improved ability to pump blood, which is essential in managing heart failure, where the heart's function is typically compromised.

An increase in cardiac output indicates that the heart is pumping more effectively and supplying adequate blood flow to meet the body’s demands, which is a desired outcome of dopamine treatment. Monitoring cardiac output provides valuable insight into the therapy's effectiveness in improving the heart's functional capacity.

Other findings, such as changes in blood pressure or heart rate, can occur but do not directly indicate the effectiveness of dopamine therapy in the context of enhancing cardiac output. The relationship between heart rate and cardiac output is more complex and can vary depending on multiple factors such as filling pressures and the patient’s underlying condition. Decreased serum potassium is also not a primary indicator of dopamine’s effectiveness and might be influenced by other medications or conditions. Thus, among the choices, increased cardiac output is the most direct and relevant measure of the therapeutic effectiveness of dopamine in heart failure patients.