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Isolated respiratory muscles weakness is an unusual presentation of Myasthenia Gravis (MG). We present a case of 49-year-old male with undiagnosed MG who presented with fluctuating dyspnea on exertion and at rest. There was no peripheral muscle involvement, diagnostic tests and standard electromyography was normal, and the serologic tests were negative. The repetitive nerve stimulation and Single Fiber Electromyography revealed the diagnosis of MG. Interestingly the patient did not have sufficient therapeutic response on first line agents and required immunoglobulins and corticosteroids due to respiratory muscle involvement. Since skeletal muscle weakness is a cardinal feature of MG, dyspnea may be fluctuating as in our patient causing further difficulty in diagnosis as the pulmonary function tests performed during remission may be normal. This presentation highlights the need to consider MG in the differential diagnosis of unexplained dyspnea on exertion/rest.