The most likely diagnosis is cardiomyopathy in this patient with systemic sclerosis. Cardiomyopathy due to systemic sclerosis–induced coronary vasospasm and microvascular disease leading to patchy myocardial fibrosis is the most common symptomatic manifestation of heart involvement in systemic sclerosis. Although accelerated macroscopic coronary atherosclerosis has been associated with other autoimmune inflammatory diseases, coronary vascular involvement in systemic sclerosis is most often microvascular, with ischemia due to structural changes and recurrent spasm of small vessels. This results in contraction band necrosis, a pathologic finding due to episodes of myocardial ischemia followed by reperfusion. This process may ultimately lead to patchy fibrosis resulting in cardiomyopathy and heart failure. Patients who have systemic sclerosis with symptomatic cardiac involvement have a poor prognosis and mortality rate of 75% at 5 years. This patient presents with evidence of fluid overload due to heart failure as seen on her physical examination and confirmed by an abnormal chest radiograph and an echocardiogram suggesting diffuse myocardial dysfunction, consistent with this cause. Infiltrative myocardial fibrosis and conduction abnormalities may also contribute to the cardiac dysfunction but are less common causes of systemic sclerosis heart disease.

Constrictive pericarditis is a chronic disorder resulting from inflammation and fibrosis of the pericardium with loss of elasticity and resulting noncompliance of the pericardium. Although it may be associated with connective tissue disease, this patient does not have specific clinical findings typically associated with constrictive pericarditis such as a pericardial knock or pulsus paradoxus; furthermore, her echocardiogram shows evidence of diffuse myocardial dysfunction and no evidence of impaired cardiac filling with normal ventricular function as would be expected with constrictive pericarditis.

Pulmonary arterial hypertension is a common complication of systemic sclerosis and may lead to cor pulmonale and primarily right-sided heart failure. This patient's clinical presentation is more consistent with generalized myocardial dysfunction due to cardiomyopathy.

The kidneys are frequently involved in systemic sclerosis, with scleroderma renal crisis (SRC) occurring in 10% to 15% of patients. SRC causes acute-onset oliguric kidney disease, severe hypertension, and often microangiopathic hemolysis and thrombocytopenia. Except for evidence of impaired kidney function likely due to heart failure, this patient's clinical presentation is not consistent with SRC.