A heart massager for substernal heart massage is disclosed. The heart massager utilizes a heart-contacting member adapted for insertion into a thoracic cavity for directly contacting the heart and a handle attached thereto for manually manipulating the apparatus. The heart-contacting member includes a cup having one end which is open and which receives the handle, and another end which is closed by an at least partially concave-shaped diaphragm which forms a heart contacting surface and allows the member to conform to the shape of the heart's surface. The ends of the cup are joined by a flexible sidewall which flares outward from the handle in its operative state. The cup's flexible sidewall allows the heart-contacting member to collapse so that it can be inserted into a relatively small incision in the chest cavity. After the heart-contacting member is inserted, fluid pressure is applied to the inside of the cup, thereby causing it to expand into its operative state.