Cardiac tumors are rare, and their treatment differs interindividually regarding the histopathological proprieties and the stage of disease. Authors present a case of symptomatic cardiac melanoma metastasis that expressed an ERBB2 (HER2) gene amplification in a course of the disease that has not yet been reported. The frail patient with a history of pulmonary and renal carcinoma, was admitted to the hospital due to a symptomatic left atrial tumor mass. The patient underwent a tumor-resecting cardiac surgery. At first mistaken for myxoma on echocardiography, the histopathological examination of the tumor revealed a melanoma of acral or mucosal origin. The melanoma metastasis was negative for common genetic mutations in BRAF, NRAS or KIT genes, and for the presence of NTRK genes fusions, but carried ERBB2 (HER2) gene amplification. The absence of standard gene mutations rendered it unresponsive to treatment with BRAF and MEK inhibitors. This molecular finding is rare in melanomas and represented a therapeutic target for off-label systemic treatment with drugs, primarily aimed at ERBB2 positive breast, gastric, and gastroesophageal junction cancers. A rare finding like this justifies molecular genetic analysis of unusual tumor specimen and guarantees optimal treatment for uncommon types of cardiac metastatic tumors.