Cardiac amyloidosis is an important cause of restrictive cardiomyopathy and congestive heart failure. Bone scintigraphy with [99mTc]hydroxymethylene diphosphonate (99mTc-HDP) and [18F]sodium fluoride (18F-NaF) have been investigated in the noninvasive diagnosis of transthyretin (ATTR)–related cardiac amyloidosis. We present a case of a 76-year-old man with metastatic prostate cancer who underwent 99mTc-HDP bone scintigraphy with an incidental finding of diffuse left ventricular abnormal uptake suggesting ATTR cardiac amyloidosis. Review of previous imaging showed a negative 18F-NaF PET/CT study. This example suggests that the mechanism of uptake of 99mTc-HDP and 18F-NaF may differ in patients with ATTR cardiac amyloidosis.