David Ortiz was admitted to Massachusetts General Hospital for evaluation. By report he had a history of palpitations, and presumably must have had documented rhythm disturbance (likely tachycardia or fast heart rate).
My comments are totally generic as I know nothing of his situation, prior health, medication use, or family history, information that his physicians will seek.
As a broad overview, tachycardia is divided between supraventricular (sinus tachycardia, atrial fibrillation and flutter, reentrant nodal rhythms) and ventricular tachycardia. As a first pass, physicians will want to know about medication use (caffeine, alcohol, cold medications, etc. - nothing to suggest cocaine or amphetamines), thyroid or other metabolic disease, and chemical balance (calcium, potassium, magnesium) and whether there are clues from the surface electrocardiogram.
Presuming the specific type of rhythm is known, physicians will try to determine whether circulatory (coronary artery disease), valvular (rheumatic or mitral valve disease), or myopathic (e.g. dilated, hypertrophic, infiltrative e.g. sarcoid or restrictive cardiomyopathy) disease exists.
In addition to heart monitoring, patients are likely to undergo transthoracic echocardiograms, ambulatory EKG monitoring, stress testing which may or may not lead to invasive testing, and if the rhythm disturbance is more severe, electrophysiologic testing. Some patients will have isolated electrical disturbances (e.g. lone atrial fibrillation), i.e. no structural, circulatory, or metabolic explanation is found.
Depending on the type of rhythm disturbance and underlying cause, there are many types of medical treatment and some types of invasive treatment. In addition to diagnosis and initial management, there will be intense examination of the patient's response to exercise, possibly under a variety of stimuli.
In treating the 'celebrity' patient, the most important elements are no different from treating all patients, trying to provide the necessary evaluation and communication to effect optimal outcome.
This is not designed to speculate on either the type of dysrhythmia or cause, but rather to provide background for readers. The evaluation is fairly standard, and we all wish the Sox slugger a speedy and full recovery.
I'm sure that we'll get whatever information the Ortiz family chooses to release, which is totally appropriate.